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  • Puzzling TCP performance over 3G / UMTS

    - by lemonsqueeze
    I'm using 3G as my primary internet connection, and TCP over this thing is getting more puzzling every day. For example: Downloading from kernel.org is crazy fast: $wget http://www.kernel.org/pub/linux/kernel/v3.0/linux-3.6.8.tar.bz2 increases to ~500kB/s after a few secs ! Some servers are incredibly slow, for instance www.graphic-pc.com:Same thing, downloading a big file with wget it starts at ~30kB/s for a split second, then collapses to 5-10k or even worse. Web browsing is decent but somewhat unreliable. Randomly, a page will take really long to load or even fail to load, but a reload can succeed almost immediately. Now, by chance i started playing with OpenVPN over UDP on top of the 3G connection, and OMG suddenly everything's extremely fast !Same www.graphic-pc.com now shoots at 100-200kB/s ! What's going on here ??? How come it is so much better with the VPN than without ?? And why does graphic-pc.com crawl when kernel.org flies ?Something to do with my tcp stack (or the server), or some buggy router in between ?? Notes: Setup is laptop running Ubuntu Lucid and a Huawei 3G dongle (So direct pppd connection). I can reproduce this pretty much any time during the day and I'm not moving, so it's clearly not cell environment or internet congestion. (although kernel.org without VPN sometimes does worse in the evening, 60kB or so - but still 500kB with VPN !) For 2) wireshark shows retransmitted packets, dup ack's, even out of order sometimes. I've tried playing with different /proc/sys/net/ipv4 parameters (tcp_rmem, window_scaling, tcp_congestion...) doesn't seem to make a difference. Update: Tried under windows 7 (no VPN) with some interesting results: tcp settings : default tcp_optimizer kernel.org : 10 kB/s 20 kB/s graphic-pc.com: 8 kB/s 70 kB/s ! tcp_optimizer turned on ctcp among other things. Have to check what os graphic-pc.com is running, my bet is linux's tcp_westwood and ms ctcp don't mix well here...

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  • TCP dies on a Linux laptop

    - by Roman Cheplyaka
    Once in several days I have the following problem. My laptop (Debian GNU/Linux testing) suddenly becomes unable to work with TCP connections to the internet. The following things continue to work fine: UDP (DNS), ICMP (ping) — I get instant response TCP connections to other machines in the local network (e.g. I can ssh to a neighbour laptop) everything is ok for other machines in my LAN But when I try TCP connections from my laptop, they time out (no response to SYN packets). Here's a typical curl output: % curl -v google.com * About to connect() to google.com port 80 (#0) * Trying 173.194.39.105... * Connection timed out * Trying 173.194.39.110... * Connection timed out * Trying 173.194.39.97... * Connection timed out * Trying 173.194.39.102... * Timeout * Trying 173.194.39.98... * Timeout * Trying 173.194.39.96... * Timeout * Trying 173.194.39.103... * Timeout * Trying 173.194.39.99... * Timeout * Trying 173.194.39.101... * Timeout * Trying 173.194.39.104... * Timeout * Trying 173.194.39.100... * Timeout * Trying 2a00:1450:400d:803::1009... * Failed to connect to 2a00:1450:400d:803::1009: Network is unreachable * Success * couldn't connect to host * Closing connection #0 curl: (7) Failed to connect to 2a00:1450:400d:803::1009: Network is unreachable Restarting the connection and/or reloading the network card kernel module doesn't help. The only thing that helps is reboot. Clearly something is wrong with my system (everything else works fine), but I have no idea what exactly. I don't know how to reproduce this, but as I said, it happens every several days. My setup is a wireless router that is connected to the ISP via PPPoE. Any advice?

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  • Datacenter IP Addressing and DNS Management

    - by user65248
    Hello everyone Basically we are setting up a small Datacenter, about 300 amps power and max 50 racks, Im saying these coz I wanna u imagine the size and requirements, I have studied networking mostly Microsoft and Windows based systems , but I cant get how the IP addressing and DNS management and configuration works in a Datacenter , and unfortunately I have to setup everything by myself but defe we will have some staff to do some job. Now my questions Datacenter IP Addressing Suppose we have got a block of 200 IP addresses from our ISP, How can I manage these block of IP addresses, is there any software out there to simplify this I heard that using DHCP server in a datacenter is not recommended, otherwise what would u say about MS DHCL server ofc considering we need to have backup serversin case of failur How can I assign a block of IPs to a specific rack, I know with different software and management its different but Im asking how it is done normally IP addresses are exposed to the whole network, what if a customer try to use an IP address and is not assigned to their server or rack , how can I prevent this or how can I track the IP usage DNS Management Im goin to setup at least two servers for our DNS servers, I know nothing about Datacenter DNS system, but I have configured DNS server in normal networks and also for webservers, Now I wanna know What exactly needs to be done for a DNS in a datacenter that is not done for normal networks. How can I configure PTR records why cant I configure PTR records on my webserver side DNS server and it should be done on datacenter DNS server , I mean what is the difference in DC DNS servers that allow us to to so , I know the question is very silly and simple but Im confused Is there any software outthere to allow doing the whole thing, I mean automatically add records to the DNS and also managin IP addresses !? Thanks in advance

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  • List Squid's internal ip:port to external ip:port mapping table

    - by joshperry
    I'm assuming that squid keeps a list of internal ip:port that a request is made on and the matching external ip:port that the request is fulfilled with. In the case of a long transfer, such as a file download, it would be nice to be able to see which internal ip:port is downloading the file. I am able to see the traffic and get the external ip:port that squid is using easily with tcpdump or iptraf but I can't find a way to map this back to an internal ip:port.

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  • Centos/OVH: public IP on KVM virtual machine

    - by Sébastien
    Since a few days, I'm trying to configure my KVM vm to have a public IP address, without any success. First, I'm on OVH, and you need to know they don't allow networking from different mac addresses. I have so registered a virtual mac address associated with my failover IP Here's my configuration: Guest wanted IP: 46.105.40.x Host IP: 176.31.240.x Host configuration dummy0 interface: ifcfg-dummy0 BOOTPROTO=static IPADDR=10.0.0.1 NETMASK=255.0.0.0 ONBOOT=yes NM_CONTROLLED=no ARP=yes BRIDGE=br0 br0 bridge: ifcfg-br0 DEVICE=br0 TYPE=Bridge DELAY=0 ONBOOT=yes BOOTPROTO=static IPADDR=192.168.1.1 NETMASK=255.255.255.0 PEERDNS=yes NM_CONTROLLED=no ARP=yes Failover ip is redirected to the br0 bridge with ip route add 46.105.40.xxx dev br0 > cat /proc/sys/net/ipv4/ip_forward 1 > cat /proc/sys/net/ipv4/conf/vnet0/proxy_arp 1 > route -n Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 176.31.240.254 0.0.0.0 UG 0 0 0 eth0 46.105.40.x 0.0.0.0 255.255.255.255 UH 0 0 0 br0 176.31.240.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 br0 Guest configuration: KVM: <interface type='bridge'> <mac address='02:00:00:30:22:05'/> <source bridge='br0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/> </interface> I've borrowed most of the OVH configuration here (in french, http://guides.ovh.com/BridgeClient) for the guest configuration eth0 interface: ifcfg-eth0 DEVICE="eth0" BOOTPROTO=none HWADDR="02:00:00:30:22:05" NM_CONTROLLED="yes" ONBOOT="yes" TYPE="Ethernet" UUID="e9138469-0d81-4ee6-b5ab-de0d7d17d1c8" USERCTL=no PEERDNS=yes IPADDR=46.105.40.xxx NETMASK=255.255.255.255 GATEWAY=176.31.240.254 ARP=yes For the routes, I have in route-eth0: 176.31.240.254 dev eth0 default via 176.31.240.254 dev eth0 With this configuration, I don't have any access to the internet. The only thing I can do is to ping the public ip of the host, nothing more. My final conclusion is that the route does not work, because, when, on the guest, I run ping 8.8.8.8, I have, on the host: > tcpdump -i vnet0 icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on br0, link-type EN10MB (Ethernet), capture size 65535 bytes 13:38:09.009324 IP 46-105-40-xxx.kimsufi.com > google-public-dns-a.google.com: ICMP echo request, id 50183, seq 1, length 64 13:38:09.815344 IP 46-105-40-xxx.kimsufi.com > google-public-dns-a.google.com: ICMP echo request, id 50183, seq 2, length 64 I never get the ping reply, only the request. It seems Guest - Host communication is fine. On eth0: > tcpdump -i eth0 icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 13:39:40.240561 IP 46-105-40-xxx.kimsufi.com > google-public-dns-a.google.com: ICMP echo request, id 50439, seq 1, length 64 13:39:40.250161 IP google-public-dns-a.google.com > 46-105-40-xxx.kimsufi.com: ICMP echo reply, id 50439, seq 1, length 64 I have the request and the reply on eth0, but reply is not forwarded to the bridge. I really don't understand why, I though it was the aim of the route to do that! IPtables is disabled on both host and guest. I really hope some of you will be able to help me! Many thanks in advance, Sébastien

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  • How can I set my linux box as a router to forward ip packets?

    - by UniMouS
    I am doing a network experiment about ip packet forwarding, but I don't know why it does work. I have a linux machine with two network interfaces, eth0 and eth1 both with static IP address (eth0: 192.168.100.1, eth1: 192.168.101.2). My goal is simple, I just want to forward ip packets from eth1 with destination in subnet 192.168.100.0/24 to eth0, and forward ip packets from eth0 with destination in subnet 192.168.101.0/24 to eth1. I turned on ip forwarding with: sysctl -w net.ipv4.ip_forward=1 my routing table is like this: # route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.100.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 192.168.101.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 But, when I try to ping from 192.168.100.25 to 192.168.101.47, it does not work.

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  • IP address reuse on macvlan devices

    - by Alex Bubnoff
    I'm trying to create easy to use and possibly simple testing environment for some product and got some strange behaviour of macvlan's. What I'm trying to achieve: make a toolset for one-line start/stop of lxc containers(via docker) bound to external ip(I have enough of it on host machine). So, I'm doing something like this: docker run -d -name=container_name container_image pipework eth1 container_name ip/prefix_len@gateway and pipework here does this: GUEST_IFNAME=ph$NSPID$eth1 ip link add link eth1 dev $GUEST_IFNAME type macvlan mode bridge ip link set eth1 up ip link set $GUEST_IFNAME netns $NSPID ip netns exec $NSPID ip link set $GUEST_IFNAME name eth1 ip netns exec $NSPID ip addr add $IPADDR dev eth1 ip netns exec $NSPID ip route delete default ip netns exec $NSPID ip link set eth1 up ip netns exec $NSPID ip route replace default via $GATEWAY ip netns exec $NSPID arping -c 1 -A -I eth1 $IPADDR And it works for first time per IP. But for second time and later packets for containers IP isn't getting into container, while all configuration seem fine. So it looks like this: External machine ? ping 212.76.131.212 ....silence.... Host machine root@ubuntu:~# ip link show eth1 2: eth1: mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 00:15:17:c9:e1:c9 brd ff:ff:ff:ff:ff:ff root@ubuntu:~# ip addr show eth1 2: eth1: mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 00:15:17:c9:e1:c9 brd ff:ff:ff:ff:ff:ff root@ubuntu:~# tcpdump -v -i eth1 icmp tcpdump: WARNING: eth1: no IPv4 address assigned tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes 00:00:46.542042 IP (tos 0x0, ttl 60, id 9623, offset 0, flags [DF], proto ICMP (1), length 84) 5.134.221.98 212.76.131.212: ICMP echo request, id 6718, seq 2345, length 64 00:00:47.549969 IP (tos 0x0, ttl 60, id 9624, offset 0, flags [DF], proto ICMP (1), length 84) 5.134.221.98 212.76.131.212: ICMP echo request, id 6718, seq 2346, length 64 00:00:48.558143 IP (tos 0x0, ttl 60, id 9625, offset 0, flags [DF], proto ICMP (1), length 84) 5.134.221.98 212.76.131.212: ICMP echo request, id 6718, seq 2347, length 64 00:00:49.566319 IP (tos 0x0, ttl 60, id 9626, offset 0, flags [DF], proto ICMP (1), length 84) 5.134.221.98 212.76.131.212: ICMP echo request, id 6718, seq 2348, length 64 00:00:50.573999 IP (tos 0x0, ttl 60, id 9627, offset 0, flags [DF], proto ICMP (1), length 84) 5.134.221.98 212.76.131.212: ICMP echo request, id 6718, seq 2349, length 64 ^C 5 packets captured 5 packets received by filter 0 packets dropped by kernel 1 packet dropped by interface Host machine, netns of container root@ubuntu:~# ip netns exec 32053 ip link show eth1 48: eth1@if2: mtu 1500 qdisc noqueue state UNKNOWN link/ether b2:12:f7:cc:a1:9d brd ff:ff:ff:ff:ff:ff root@ubuntu:~# ip netns exec 32053 ip addr show eth1 48: eth1@if2: mtu 1500 qdisc noqueue state UNKNOWN link/ether b2:12:f7:cc:a1:9d brd ff:ff:ff:ff:ff:ff inet 212.76.131.212/29 scope global eth1 inet6 fe80::b012:f7ff:fecc:a19d/64 scope link valid_lft forever preferred_lft forever root@ubuntu:~# ip netns exec 32053 tcpdump -v -i eth1 icmp tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes ....silence.... ^C 0 packets captured 0 packets received by filter 0 packets dropped by kernel So, can anyone say, what can it be? Can this be caused by not a bug in macvlan implementation? Is there any tools I can use to debug that configuration?

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  • tcp connect hangs on SYN_SENT if something listens, gets CONN_REFUSED if nothing listens

    - by Amos Shapira
    I'm hitting a very strange problem - when I try to connect to one of our servers the client hangs with SYN_SENT if something listens on the port (e.g. Apache on port 80, sshd on port 22 or SMTP on port 25) but if I try to connect to a port on which nothing listens then I immediately get a "CONNECTION refused" error. Connecting to other applications (e.g. rsyncd on some arbitrary port) succeeds. I ran tcpdump on the server and see that the SYN packets arrive to it but it only sends a response if nothing listens on that port. e.g.: on the server I run: # tcpdump -nn port 81 06:49:34.641080 IP 10.x.y.z.49829 server.81: S 3966400723:3966400723(0) win 12320 06:49:34.641118 IP server.81 x.y.z.49829: R 0:0(0) ack 3966400724 win 0 But if I listen on this port, e.g. with nc -4lvvv 81 & Then the output of tcpdump is: 06:44:31.063614 IP x.y.z.45954 server.81: S 3493682313:3493682313(0) win 12320 (and repeats until I stop it) The server is CentOS 5, the client is Ubuntu 11.04, the connection is done between two LAN's over per-user TCP OpenVPN. Connection to other servers on that network do not have a problem. Connecting from the other servers on the same network to that server works fine. Connections from other clients in our office over openvpn is also not a problem. What am I missing? Thanks.

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  • How to transition to Comcast with static IP address

    - by steveha
    I have my own email server in my house, on a static IP address. I have had business DSL for over a decade, but I also now have Comcast business Internet. I want to transition from the DSL to the Comcast, and I have some questions. I have a domain name, my own mail server, and a firewall (a PC with two network interfaces, running Devil-Linux). I need to make sure I understand how to set up the Comcast cable box, and how to set up my firewall. First, do I need to change any settings in the cable box? Currently I have only used the cable box by plugging in a laptop, with the laptop doing DHCP. I think I can leave the box alone but I would like to make sure. Second, I'm not sure I understand the instructions Comcast gave me for setting up the firewall. My DSL provider gave me the following information: static IP address, net mask, gateway, and two DNS servers. Comcast gave me: static IP address, routable static IP address, net mask, and two DNS servers, and told me to put the "static IP address" as the "gateway" on the firewall. Is this just Comcast-speak here? Does "routable static IP address" mean the same thing as "static IP address" in my DSL setup, the end-point address that I should publish in the DNS MX records for my email server? Or should I publish the "static IP address", and Comcast will then route all its traffic over the cable box? My plan is: first, I'm going to configure another firewall, so I have one firewall for the DSL and one for the Comcast (rather than madly editing settings to switch back and forth). Then I will publish the new Comcast static IP address as a backup email server address in the DNS MX records, wait a while to let it propagate, and then switch my home over from the DSL to the Comcast. Then I'll change DNS to make that the primary mail address and the DSL the secondary, let that go a while and make sure it seems reliable. Then I'll remove the DSL from the DNS MX records completely, and finally shut down the DSL service. (I thought about keeping the DSL as a backup, but the reason I'm leaving DSL is that it has become unreliable; and I have heard that Comcast business Internet is reliable.) Final question, any advice for me? Anything you think might be useful, helpful, or educational. Thanks.

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  • How to transition to Comcast with static IP address [migrated]

    - by steveha
    I have my own email server in my house, on a static IP address. I have had business DSL for over a decade, but I also now have Comcast business Internet. I want to transition from the DSL to the Comcast, and I have some questions. I have a domain name, my own mail server, and a firewall (a PC with two network interfaces, running Devil-Linux). I need to make sure I understand how to set up the Comcast cable box, and how to set up my firewall. First, do I need to change any settings in the cable box? Currently I have only used the cable box by plugging in a laptop, with the laptop doing DHCP. I think I can leave the box alone but I would like to make sure. Second, I'm not sure I understand the instructions Comcast gave me for setting up the firewall. My DSL provider gave me the following information: static IP address, net mask, gateway, and two DNS servers. Comcast gave me: static IP address, routable static IP address, net mask, and two DNS servers, and told me to put the "static IP address" as the "gateway" on the firewall. Is this just Comcast-speak here? Does "routable static IP address" mean the same thing as "static IP address" in my DSL setup, the end-point address that I should publish in the DNS MX records for my email server? Or should I publish the "static IP address", and Comcast will then route all its traffic over the cable box? My plan is: first, I'm going to configure another firewall, so I have one firewall for the DSL and one for the Comcast (rather than madly editing settings to switch back and forth). Then I will publish the new Comcast static IP address as a backup email server address in the DNS MX records, wait a while to let it propagate, and then switch my home over from the DSL to the Comcast. Then I'll change DNS to make that the primary mail address and the DSL the secondary, let that go a while and make sure it seems reliable. Then I'll remove the DSL from the DNS MX records completely, and finally shut down the DSL service. (I thought about keeping the DSL as a backup, but the reason I'm leaving DSL is that it has become unreliable; and I have heard that Comcast business Internet is reliable.) Final question, any advice for me? Anything you think might be useful, helpful, or educational. Thanks.

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  • Multiple IP addresses to one NIC, but advanced IP settings window only shows one?

    - by tridium
    The ipconfig of my Windows Server 2003 server shows that the IP addresses 10.0.0.3, 10.0.0.11, and 10.0.0.12 are assigned to it. However, when I look in the Advanced TCP/IP Settings window for that connection, I only see the IP address of 10.0.0.3 listed there. In the Support tab for the connection, it shows that it's connected through 10.0.0.12, and in the Support Details window, it shows all the previously mentioned IP addresses. Where are these phantom IP addresses being stored and how can I free them up so I don't have any IP conflicts?

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  • Confusion about TCP packet analysis terms

    - by Berkay
    I'm analyzing our network and have some confusion about the terms: this is the 2-packet output from source to destination. from these i have to get some features as describe, pls make me clear... packets with at least a bytes of TCP data payload: it seems tcp.len0; The minimum segment size (confusion is headers are included or or not) The average segment size observed during the lifetime of the connection, the definition: is calculated as the value reported in the actual data bytes divided by the actual data pkts reported. Total bytes in IP packets, should be ip_len value. Total bytes in (Ethernet) The total number of bytes sent probably related to frame.len and frame.cap_len these two terms are describes as, also make me clear about these two terms. frame.cap_len: Frame length stored into the capture file frame.len: Frame length on the wire

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  • How can private IPV4 addresses get past iptables NAT (tcp RST,FIN)

    - by gscott
    I've got a router performing simple NAT translation using iptables iptables -t nat -o -j MASQUERADE This works fine almost all of the time except for one particular case where some TCP RST and FIN packets are leaving the router un-NAT'd. In this scenario I setup 1 or 2 client computers streaming Flash video (eg www.nasa.gov/ntv) At the router I then tear down and re-establish the public interface (which is a modem) As expected the Flash streams stall out. After the connection is re-established and I try to refresh the Flash pages, I see some TCP RST and [FIN,ACK] packets leaving the public interface (I assume as Flash attempts to recover its stream). I don't know how these packets can leave the router non-NAT'd

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  • Will I need a dedicated static IP or a unique IP is enough to SSL enable my website?

    - by Devner
    Hi, This is the first time I am dealing with SSL and Dedicated Static IP /Unique IP. Now this webhost says that they will provide Unique IP (not shared with other customers) but do NOT guarantee that it will be static. Now I plan to make my website SSL enabled and install a SSL certificate. So in order to SSL enable my website, will I really need a Dedicated Static IP or will this Unique IP (without the guarantee that it will be static) be enough? What problems will I need to face if the IP is not static? I have already bought hosting from them. And they showed me that option while adding optional services to the account (after I placed my order), so I did not even have a clue about this. Thank you all in advance.

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  • IP Camera working on lan but not on internet

    - by Kevin Boyd
    My IP cam model is Genius 350TR, I tested the cam at home on lan and internet and it worked. Then I shifted it to an office. It works on the office lan setup but I cannot connect to the ip cam from home. The IP cam is configured for port 192.168.0.30:7070 and it has a port forwarded to publicIP:7071 When I telnet to that public IP it connects to that port. However when I try to access the ip cam from a web browser it only shows me the configuration page and settings and the video is blank and it says connecting for some time and then says disconnected. The cam is configured for HTTP on internet and UDP on Lan. The office setup is ISP --- WifiRouter --- PC With Wifi card --- Switch --- IP CAM Is there a way to debug this problem?

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  • terminal tools and logs for debugging TCP issues

    - by kellogs
    I have a server which I am testing for functionality (not load, not stress) with tsung. 50 users / second, 100 total users. Judging from tsung (tsung is the testing framework) graphs, there TCP connections (red line) drops to 0 while the commenced user sessions (green line) does not. Server logs show nothing to be gripping onto, so I am speculating some kind of TCP issue. Should this be the case ? Where would I look further on the server, any logs / tools to be looking at ? Only SSH available, no GUI. > root@XMPP:~# cat /etc/lsb-release > DISTRIB_ID=Ubuntu > DISTRIB_RELEASE=11.10 > DISTRIB_CODENAME=oneiric > DISTRIB_DESCRIPTION="Ubuntu 11.10" Thank you

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  • VMWare Hypervisor vSphere 5 - VM static ip from VLAN NAT

    - by Ian Livingstone
    I have a VMWare vSphere 5 Hypervisor server that has a static ip address assigned to it by VLAN that is configured to perform NAT. The static IP is assigned to the bare metal server via the NIC's mac address. I want to setup a guest machine to also have a static ip address, how can I go about having this setup? I have assigned a IP for the guest's MAC Address but it doesn't seem to be working as when I ping the ip address it does not respond. The guest is running ubuntu 10.04 server edition. I am trying to assign it a static public ip address. Any help would be greatly appreciated.

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  • Windows Server 2008 constantly spamming external IP's on outbound TCP port 445

    - by RSXAdmin
    Hi Server Fault, I have a Windows Server 2008 box running as a Domain Controller. I have noticed in my Cisco ASA firewall logs that this box is continuously sending out (like a thousand requests a second) requests on TCP port 445 to external hosts. I have made an effort to deny this outbound traffic from getting on the internet (using the ASA), however I would like these requests to stop from even occurring at all. I have tried disabling TCP/IP over NetBIOS. I have even turned on Windows Advanced Firewall on the box itself to block outbound 445 but the ASA still detects this particular traffic hitting it. I have other DC's and similar type boxes which are not behaving the same way as this box. Is this normal? Is there a way to stop this spamming? Have I been infected? Thank you universe.

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  • TCP 30 small packets per second flood connection with server

    - by Denis Ermolin
    I'm testing connection with flash client and cloud server(boost::asio for software) over TCP connection. My connection with server already is really poor - 120 ms ping in average. I found when i start to send packets with 2 bytes size (without tcp header) with speed 30 packets/s - ping grow to 170-200 average. I think that it's really bad and my bad connection and bad cloud provider is reason for this high ping without any load. What do you think? (I tested my software - it can compute about 50k small packets/s so software is not a problem). I measure my ping through flash client - send packet with timestamp and immediatly send from server to client.

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  • Tcp window size won't go above 130048

    - by Roger
    I have 2 servers set up with about 80ms latency between them. Both are centos 6 and run a java app that transfers data from on location to another. Both are on 1gbps connections. I have been trying different sysctl settings and different send & receive buffer settings in java but no matter what I set them to, I cannot get the tcp window size to go above 130048 in the tcp dumps. This equates to roughly 13mbps which is the actual throughput I am getting.

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  • Poor TCP loopback throughput on Windows

    - by Yodan Tauber
    I measured the throughput of a locally bound TCP socket connection on my computer (Intel Q9550, 64 GB RAM, Windows XP 64 bit) using iperf. I got dissatisfying results (around 1.6 Gbit/s) each time, no matter how I tweaked the TCP settings (buffer length, window size, max segment size, no delay). I got similar results when I tried netperf. Now, I understand (from sources like these) that the average throughput of a loopback connection should be around 5 Gbit/s. What could be the reasons for such poor performance?

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  • DTracing TCP congestion control

    - by user12820842
    In a previous post, I showed how we can use DTrace to probe TCP receive and send window events. TCP receive and send windows are in effect both about flow-controlling how much data can be received - the receive window reflects how much data the local TCP is prepared to receive, while the send window simply reflects the size of the receive window of the peer TCP. Both then represent flow control as imposed by the receiver. However, consider that without the sender imposing flow control, and a slow link to a peer, TCP will simply fill up it's window with sent segments. Dealing with multiple TCP implementations filling their peer TCP's receive windows in this manner, busy intermediate routers may drop some of these segments, leading to timeout and retransmission, which may again lead to drops. This is termed congestion, and TCP has multiple congestion control strategies. We can see that in this example, we need to have some way of adjusting how much data we send depending on how quickly we receive acknowledgement - if we get ACKs quickly, we can safely send more segments, but if acknowledgements come slowly, we should proceed with more caution. More generally, we need to implement flow control on the send side also. Slow Start and Congestion Avoidance From RFC2581, let's examine the relevant variables: "The congestion window (cwnd) is a sender-side limit on the amount of data the sender can transmit into the network before receiving an acknowledgment (ACK). Another state variable, the slow start threshold (ssthresh), is used to determine whether the slow start or congestion avoidance algorithm is used to control data transmission" Slow start is used to probe the network's ability to handle transmission bursts both when a connection is first created and when retransmission timers fire. The latter case is important, as the fact that we have effectively lost TCP data acts as a motivator for re-probing how much data the network can handle from the sending TCP. The congestion window (cwnd) is initialized to a relatively small value, generally a low multiple of the sending maximum segment size. When slow start kicks in, we will only send that number of bytes before waiting for acknowledgement. When acknowledgements are received, the congestion window is increased in size until cwnd reaches the slow start threshold ssthresh value. For most congestion control algorithms the window increases exponentially under slow start, assuming we receive acknowledgements. We send 1 segment, receive an ACK, increase the cwnd by 1 MSS to 2*MSS, send 2 segments, receive 2 ACKs, increase the cwnd by 2*MSS to 4*MSS, send 4 segments etc. When the congestion window exceeds the slow start threshold, congestion avoidance is used instead of slow start. During congestion avoidance, the congestion window is generally updated by one MSS for each round-trip-time as opposed to each ACK, and so cwnd growth is linear instead of exponential (we may receive multiple ACKs within a single RTT). This continues until congestion is detected. If a retransmit timer fires, congestion is assumed and the ssthresh value is reset. It is reset to a fraction of the number of bytes outstanding (unacknowledged) in the network. At the same time the congestion window is reset to a single max segment size. Thus, we initiate slow start until we start receiving acknowledgements again, at which point we can eventually flip over to congestion avoidance when cwnd ssthresh. Congestion control algorithms differ most in how they handle the other indication of congestion - duplicate ACKs. A duplicate ACK is a strong indication that data has been lost, since they often come from a receiver explicitly asking for a retransmission. In some cases, a duplicate ACK may be generated at the receiver as a result of packets arriving out-of-order, so it is sensible to wait for multiple duplicate ACKs before assuming packet loss rather than out-of-order delivery. This is termed fast retransmit (i.e. retransmit without waiting for the retransmission timer to expire). Note that on Oracle Solaris 11, the congestion control method used can be customized. See here for more details. In general, 3 or more duplicate ACKs indicate packet loss and should trigger fast retransmit . It's best not to revert to slow start in this case, as the fact that the receiver knew it was missing data suggests it has received data with a higher sequence number, so we know traffic is still flowing. Falling back to slow start would be excessive therefore, so fast recovery is used instead. Observing slow start and congestion avoidance The following script counts TCP segments sent when under slow start (cwnd ssthresh). #!/usr/sbin/dtrace -s #pragma D option quiet tcp:::connect-request / start[args[1]-cs_cid] == 0/ { start[args[1]-cs_cid] = 1; } tcp:::send / start[args[1]-cs_cid] == 1 && args[3]-tcps_cwnd tcps_cwnd_ssthresh / { @c["Slow start", args[2]-ip_daddr, args[4]-tcp_dport] = count(); } tcp:::send / start[args[1]-cs_cid] == 1 && args[3]-tcps_cwnd args[3]-tcps_cwnd_ssthresh / { @c["Congestion avoidance", args[2]-ip_daddr, args[4]-tcp_dport] = count(); } As we can see the script only works on connections initiated since it is started (using the start[] associative array with the connection ID as index to set whether it's a new connection (start[cid] = 1). From there we simply differentiate send events where cwnd ssthresh (congestion avoidance). Here's the output taken when I accessed a YouTube video (where rport is 80) and from an FTP session where I put a large file onto a remote system. # dtrace -s tcp_slow_start.d ^C ALGORITHM RADDR RPORT #SEG Slow start 10.153.125.222 20 6 Slow start 138.3.237.7 80 14 Slow start 10.153.125.222 21 18 Congestion avoidance 10.153.125.222 20 1164 We see that in the case of the YouTube video, slow start was exclusively used. Most of the segments we sent in that case were likely ACKs. Compare this case - where 14 segments were sent using slow start - to the FTP case, where only 6 segments were sent before we switched to congestion avoidance for 1164 segments. In the case of the FTP session, the FTP data on port 20 was predominantly sent with congestion avoidance in operation, while the FTP session relied exclusively on slow start. For the default congestion control algorithm - "newreno" - on Solaris 11, slow start will increase the cwnd by 1 MSS for every acknowledgement received, and by 1 MSS for each RTT in congestion avoidance mode. Different pluggable congestion control algorithms operate slightly differently. For example "highspeed" will update the slow start cwnd by the number of bytes ACKed rather than the MSS. And to finish, here's a neat oneliner to visually display the distribution of congestion window values for all TCP connections to a given remote port using a quantization. In this example, only port 80 is in use and we see the majority of cwnd values for that port are in the 4096-8191 range. # dtrace -n 'tcp:::send { @q[args[4]-tcp_dport] = quantize(args[3]-tcps_cwnd); }' dtrace: description 'tcp:::send ' matched 10 probes ^C 80 value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@ 5 1 | 0 2 | 0 4 | 0 8 | 0 16 | 0 32 | 0 64 | 0 128 | 0 256 | 0 512 | 0 1024 | 0 2048 |@@@@@@@@@ 8 4096 |@@@@@@@@@@@@@@@@@@@@@@@@@@ 23 8192 | 0

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