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• What is needed to use anycast IPs?

  - by coredump

  So, there're a bunch of questions on SF about the uses and how anycast IPs are cool. My approach is something more practical. What specifically I need to have to use one of those addresses? Do I need to be an AS (Autonomous System)? If I want to use an Anycast IP on my internal network, is it possible? Do I need anything special with a registrar/operator(s) to use it? Basically, if I want to use an Anycast IP address, what exactly I need, from the equipment to configuration part.

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• Network Load Balancing and AnyCast Routing

  - by user126917

  Hi All can anyone advise on problems with the following? I am planning on installing the following setup on my estate: I have 2 sites that both have a large amount of users. Goals are to keep things simple for the users and to have automatic failover above the database level. Our Database will exist at the primary site and be async mirrored to the secondary site with manual failover procedures.The database generate sequential ID's so distributing it is not an option. I plan to site IIS boxes at both sites with all of the business logic on them and heavy operations. The connections to SQL will be lightweight and DB reads will be cached on IIS. On this layer I plan to use Windows network load balancing and have the same IP or IPs across all IIS boxes at both sites. This way there will be automatic failover and no single point of failure. Also users can have one web address regardless of which site they are in automatically be network load balanced to their local IIS. This is great but obviously our two sites are on different subnets and as this will be one IP address with most of our traffic we can't go broadcasting everything across the link between the sites. To solve this problem we plan to use AnyCast routing over our network layer to route the traffic to the most local box that is listening which will be defined by the network load balancing. Has anyone used this setup before? Can anyone think of any issues with this? Also some specifics I can't find anywhere at the moment. If my Windows box is assigned an IP and listening on that IP but network load balancing is not accepting specific traffic then will AnyCast route away from that? Also can I AnyCast on a socket level?

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• Is this anycast behaviour correct?

  - by etheros

  When connecting to an service provided using anycast, I am experiencing different behaviour depending on whether the request is made using TCP or UDP. With TCP, the request is made to address A, and the subsequent response also comes from A. With UDP however, while the request is made to A, the response comes from address B. Is this correct behaviour, or should the UDP response come from the same address it's sent to?

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• What is the difference between Anycast and GeoDNS / GeoIP wrt HA?

  - by Riyad

  Based on the Wikipedia description of Anycast, it includes both the distribution of a domain-name-to-many-IP-mapping across many DNS servers as well as replying to clients with the most geographically close (or fastest) server. In the context of a globally distributed, highly available site like google.com (or any CDN service with many global edge locations) this sounds like the two key features one would need. DNS services like Amazon's Route53, EasyDNS and DNSMadeEasy all advertise themselves as Anycast-enabled networks. Therefore my assumption is that each of these DNS services transparently offer me those two killer features: multi-IP-to-domain mapping AND routing clients to the closest node. However, each of these services seem to separate out these two functionalities, referring to the 2nd one (routing clients to closest node) as "GeoDNS", "GeoIP" or "Global Traffic Director" and charge extra for the service. If a core tenant of an Anycast-capable system is to already do this, why is this functionality being earmarked as this extra feature? What is this "GeoDNS" feature doing that a standard Anycast DNS service won't do (according to the definition of Anycast from Wikipedia -- I understand what is being advertised, just not why it isn't implied already). I get extra-confused when a DNS service like Route53 that doesn't support this nebulous "GeoDNS" feature lists functionality like: Fast – Using a global anycast network of DNS servers around the world, Route 53 is designed to automatically route your users to the optimal location depending on network conditions. As a result, the service offers low query latency for your end users, as well as low update latency for your DNS record management needs. ... which sounds exactly like what GeoDNS is intended to do, but geographically directing clients is something they explicitly don't support it yet. Ultimately I am looking for the two following features from a DNS provider: Map multiple IP addresses to a single domain name (like google.com, amazon.com, etc. does) Utilize a DNS service that will respond to client requests for that domain with the IP address of the nearest server to the requestee. As mentioned, it seems like this is all part of an "Anycast" DNS service (all of which these services are), but the features and marketing I see from them suggest otherwise, making me think I need to learn a bit more about how DNS works before making a deployment choice. Thanks in advance for any clarifications.

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• What's the piece of hardware listening on Facebook's or Wikipedia's IP address?

  - by Igor Ostrovsky

  I am trying to understand how massive sites like Facebook or Wikipedia work, for my intellectual curiosity. I read about various techniques for building scalable sites, but I am still puzzled about one particular detail. The part that confuses me is that ultimately, the DNS will map the entire domain to a single IP address, or a handful of IP addresses in the case of round-robin DNS. For example, wikipedia.org has only one type-A DNS record. So, people from all over the world visiting Wikipedia have to send a request to the one IP address specified in DNS. What is the piece of hardware that listens on the IP address for a massive site, and how can it possibly handle all the load coming from the requests for users all over the world? Edit 1: Thanks for all the responses! Anycast seems like a feasible answer... Does anyone know of a way to check whether a particular IP address is anycast-routed, so that I could verify that this really is the trick used in practice by large sites? Edit 2: After more reading on the topic, it appears that anycast is not typically used for dynamic web content. Anycast is usually used for UDP (e.g., DNS lookups), or sometimes for static content. One interesting thing to note is that Facebook uses profile.ak.fbcdn.net to host static content like style sheets and javascript libraries. Each time I ping this name, I get a response from a different IP address. However, I can't tell whether this is anycast in action, or a completely different technique. Back to my original question: as far as I can tell, even a large site will have a single expensive piece of load-balancing hardware listening on its handful of public IP addresses.

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• Multiple data centers and HTTP traffic: DNS Round Robin is the ONLY way to assure instant fail-over?

  - by vmiazzo

  Hi, Multiple A records pointing to the same domain seem to be used almost exclusively to implement DNS Round Robin as a cheap load balancing technique. The usual warning against DNS RR is that it is not good for high availability. When 1 IP goes down clients will continue to use it for minutes. A load balancer is often suggested as a better choice. Both claims are not completely true: When the traffic is HTTP then, most of the HTML browsers are able to automatically try the next A record if the previous is down, without a new DNS look-up. Read here chapter 3.1 and here. When multiple data centers are involved then, DNS RR is the only option to distribute traffic across them. So, is it true that, with multiple data centers and HTTP traffic, the use of DNS RR is the ONLY way to assure instant fail-over when one data center goes down? Thanks, Valentino Edit: Off course each data center has a local Load Balancer with hot spare. It's OK to sacrifice session affinity for an instant fail-over. AFAIK the only way for a DNS to suggest a data center instead of another is to reply with just the IP (or IPs) associated to that data center. If the data center becomes unreachable then all those IP are also unreachables. This means that, even if smart HTML browsers are able to instantly try another A record , all the attempts will fail until the local cache entry expires and a new DNS lookup is done, fetching the new working IPs (I assume DNS automatically suggests to a new data center when one fail). So, "smart DNS" cannot assure instant fail-over. Conversely a DNS round-robin permits it. When one data center fail, the smart HTML browsers (most of them) instantly try the other cached A records jumping to another (working) data center. So, DNS round-robin doesn't assure session affinity or the lowest RTT but seems to be the only way to assure instant fail-over when the clients are "smart" HTML browsers. Edit 2: Some people suggest TCP Anycast as a definitive solution. In this paper (chapter 6) is explained that Anycast fail-over is related to BGP convergence. For this reason Anycast can employ from 15 minutes to 20 seconds to complete. 20 seconds are possible on networks where the topology was optimized for this. Probably just CDN operators can grant such fast fail-overs. Edit 3:* I did some DNS look-ups and traceroutes (maybe some expert can double check) and: The only CDN using TCP Anycast seems to be CacheFly, other operators like CDN networks and BitGravity use CacheFly. Seems that their edges cannot be used as reverse proxies. Therefore, they cannot be used to grant instant failover. Akamai and LimeLight seems to use geo-aware DNS. But! They return multiple A records. From traceroutes seems that the returned IPs are on the same data center. So, I'm puzzled on how they can offer a 100% SLA when one data center goes down.

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• DNS servers via RA in IPv6

  - by glglgl

  Some time ago, RFC 6106 was created, which states how a router tells the clients about the DNS server to be used. It is a new standard, it has to be implemented, which needs time etc. I'm courious about the need for it: wouldn't have it been better to define a "globally valid" anycast address for DNS? Queries would be sent to this address and would be promoted along the default route until there is a host which claims to be responsible for it. In an enterprise network, that would be a central DNS server (or even more, on really big companies); in a SOHO network, it would either be the router or the DNS server of the ISP, in a root server hosting data center, it would be the DNS of the hoster, etc. What do I see wrong here? Do I have a wrong view of the anycast concept?

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• DNS Resolver Speed Techniques

  - by Rob Olmos

  I recently received a reply to my concerns about some DNS servers being slower than others despite all servers being anycast: In practice, most resolvers won't be impacted by the slower paths to some of the name servers in the set. Most resolvers employ various techniques to provide fast lookups, such as preferring name servers that were previously seen to be faster, sending simultaneous queries to multiple name servers, or pre-fetching queries before the TTL has expired. I was not aware that resolvers used these techniques and I was unsuccessful at searching for more info about this. Are there any names for these techniques? Which resolvers employ which of these techniques?

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• What is the best server or Ip address to use for prolonged testing?

  - by eldorel

  I usually run uptime/latency tests against (and from) two servers that we own at different sites and until recently I've used the google dns servers as a control group. However, I've realized there is a potential problem with monitoring latency over extended periods of time. Almost all of the major service providers are using ANYCAST. For short tests this doesn't matter, but I need to run a set of tests for at least a week to try and catch an intermittent problem, and a change in the anycast priority while trying to test latency will cause the latency values for that server to change accordingly. Since I'm submitting graphs of this data to the ISP, I need to avoid/account for as many variables as possible. Spikes in the data for only one of the tested servers will only cause headaches. So can anyone recommend servers that: are not using anycast are owned by an entity that has a good uptime reputation (so they can't claim that the problem is server-side) will respond to ICMP requests Have an available service that runs on TCP/UDP (http or dns preferably) Wont consider an automated request every 10 minutes to be abuse Are accessible from anywhere in the world Are not local to the isp ( consider this an investigation of a hostile party ) Thanks in advance. Edit: added #6 and #7 above. More info: I am attempting to demonstrate a network problem for an entire node of our local ISP's network. They are actively blaming the issue on the equipment installed at the customer sites (our backup site is one of these), and refuse to escalate the problem. (even though 2 of these businesses have ISP provided modems, and all of us have completely different routers/services running) I am already quite familiar with the need to test an isp controlled IP, but they are actively dropping all packets targeted at gateway ip addresses and are only passing traffic addressed beyond the gateways. So to demonstrate the issue, I am sending packets to other systems in the same node, systems one hop away from the affected node, and systems completely outside the network. Unfortunately, all of the systems I have currently are either administered directly by myself, or by people who are biased enough to assist me. I need to have several systems included in the trace/log/graphs that are 100% not in the control of either myself or the isp so that the graphs have a stable/unbiased control group. These requirements are straight from legal, I'm just trying to make sure that everything that could be argued to invalidate the data is already covered. In Summary: I need to be able to show tcp/udp/icmp as 3 separate data points, and I need to be able to show the connections inside the local node, from local node to another nearby node, from those 2 nodes to the internet, and through the internet to both verifiable servers and a control group that I have no control over whatsoever. Again, Google/opendns/yahoo/msn/facebook/etc all use anycast, which throws the numbers off every time the anycast caches expire, so I need suggestions of an IP or server that is available for this type of testing. I was hoping someone knew of a system run by someone such as ISC or ICANN, or perhaps even a .gov server (fcc or nsa maybe?) setup for this type of testing. Thanks again.

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• What is good usage scenario for Rackspace Cloud Files CDN (powered by AKAMAI) [closed]

  - by Andrew Smith

  I have just setup my website as static page via Rackspace CDN / Akamai. www.example.co.uk is an alias for d9771e6f24423091aebc-345678991111238fabcdef6114258d0e1.r61.cf3.rackcdn.com. d9771e6f24423091aebc-345678991111238fabcdef6114258d0e1.r61.cf3.rackcdn.com is an alias for a61.rackcdn.com. a61.rackcdn.com is an alias for a61.rackcdn.com.mdc.edgesuite.net. a61.rackcdn.com.mdc.edgesuite.net is an alias for a63.dscg10.akamai.net. a63.dscg10.akamai.net has address 63.166.98.41 a63.dscg10.akamai.net has address 63.166.98.40 a63.dscg10.akamai.net has IPv6 address 2001:428:4c02::cda8:ecb9 a63.dscg10.akamai.net has IPv6 address 2001:428:4c02::cda8:ed09 The HTTP header: HTTP/1.0 200 OK Last-Modified: Fri, 19 Oct 2012 23:27:41 GMT ETag: fdf9e14b77def799e09e8ce815a521da X-Timestamp: 1350689261.23382 Content-Type: text/html X-Trans-Id: tx457979be3bd746c2b4e5403a1189cdbc Cache-Control: public, max-age=900 Expires: Sat, 27 Oct 2012 22:18:56 GMT Date: Sat, 27 Oct 2012 22:03:56 GMT Content-Length: 7124 Connection: keep-alive I am wondering, if it's really the fastest solution to power the website? By investigating it thru http://www.just-ping.com/ it seems, that from many places the ping is very high, and during quick investigation I found that they use GeoIP to resolve addresses based on WHOIS, which is not accurate and because of that from many places the ping is above 300ms (for example, if ISP is in balgladore and request is routed to bangladore even if it's 300ms, for period of 1 month), while by just using Amazon Web Services and Route 53 Anycast DNS servers and only 4 EC2 instances it seems that for example India is always below 100ms, while using Akamai it goes above 300ms in some cases, and this is because Route 53 is using BGP. By quickly checking the Akamai, it seems that they are not getting feedback from the traffic - the high ping stays constant even if I keep downloading large files and videos, which is opposite to what they say on their website. They state, that they optimize the performance by taking feedback from the requests, while it seems they just use GeoIP with per City resolution (which are mostly big cities). Because of this, AWS with Route 53 / Anycast DNS seems to be much more reliable, as well EdgeCast which is using BGP, but I dont know how much does it cost to deploy static website. Actually, I dont know if EdgeCast is not a lie, because from isolated places there are many errors - so their performance is at the cost of quality of delivery, because of BGP switching the routes during transfer of large files. So I was wondering, what is really Akamai good for, because they dont seem to pose any strength in any field in what I do understand now, except they offer some software based WAF on their website, but what I really care about is the core distribiution, so the question is? Is really Akamai good for Videos? For static websites? ??? I found so far AWS most usable with most consistent ping and stable transfers.

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• Best criteria for choosing a DNS provider : Redundancy, Locations, Cost, IPV6, Reliability

  - by antoinet

  What criteria should I use to choose a good DNS provider? Redundancy - Your DNS service should use at least 4 nameservers. You should also check for the use of anycast servers such as Amazon Route 53 and dyn.com services. Worldwide server location - Servers shall be located worldwide, not just in one country! Ipv6 support - It shall be possible to declare an AAAA entry to your server if it supports IPV6 Cost is of course an issue. Some service are free, Amazon Route 53 seems quite cheap. Reliability : SLA is also important, it demonstrate that reliability is measured. Your dns provider shall then state for a refund in case a failure is encountered. Anything else? For reference, a couple of links for more information: http://serverfault.com/questions/216330/why-should-i-use-amazon-route-53-over-my-registrars-dns-servers http://aws.amazon.com/route53/ http://dyn.com/dns/

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• Weighted round robins via TTL - possible?

  - by Joe Hopfgartner

  I currently use DNS round robin for load balancing, which works great. The records look like this (I have a ttl of 120 seconds) ;; ANSWER SECTION: orion.2x.to. 116 IN A 80.237.201.41 orion.2x.to. 116 IN A 87.230.54.12 orion.2x.to. 116 IN A 87.230.100.10 orion.2x.to. 116 IN A 87.230.51.65 I learned that not every ISP / device treats such a response the same way. For example some DNS servers rotate the addresses randomly or always cycle them through. Some just propagate the first entry, others try to determine which is best (regionally near) by looking at the ip address. However if the userbase is big enough (spreads over multiple ISPs etc) it balances pretty well. The discrepancies from highest to lowest loaded server hardly every exceeds 15%. However now I have the problem that I am introducing more servers into the systems, that not all have the same capacities. I currently only have 1gbps servers, but I want to work with 100mbit and also 10gbps servers too. So what I want is I want to introduce a server with 10 GBps with a weight of 100, a 1 gbps server with a weight of 10 and a 100 mbit server with a weight of 1. I used to add servers twice to bring more traffic to them (which worked nice. the bandwidth doubled almost.) But adding a 10gbit server 100 times to DNS is a bit rediculous. So I thought about using the TTL. If I give server A 240 seconds ttl and server B only 120 seconds (which is about about the minimum to use for round robin, as a lot of dns servers set to 120 if a lower ttl is specified.. so i have heard) I think something like this should occour in an ideal scenario: first 120 seconds 50% of requests get server A -> keep it for 240 seconds. 50% of requests get server B -> keep it for 120 seconds second 120 seconds 50% of requests still have server A cached -> keep it for another 120 seconds. 25% of requests get server A -> keep it for 240 seconds 25% of requests get server B -> keep it for 120 seconds third 120 seconds 25% will get server A (from the 50% of Server A that now expired) -> cache 240 sec 25% will get server B (from the 50% of Server A that now expired) -> cache 120 sec 25% will have server A cached for another 120 seconds 12.5% will get server B (from the 25% of server B that now expired) -> cache 120sec 12.5% will get server A (from the 25% of server B that now expired) -> cache 240 sec fourth 120 seconds 25% will have server A cached -> cache for another 120 secs 12.5% will get server A (from the 25% of b that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of b that now expired) -> cache 120 secs 12.5% will get server A (from the 25% of a that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of a that now expired) -> cache 120 secs 6.25% will get server A (from the 12.5% of b that now expired) -> cache 240 secs 6.25% will get server B (from the 12.5% of b that now expired) -> cache 120 secs 12.5% will have server A cached -> cache another 120 secs ... i think i lost something at this point but i think you get the idea.... As you can see this gets pretty complicated to predict and it will for sure not work out like this in practice. But it should definitely have an effect on the distribution! I know that weighted round robin exists and is just controlled by the root server. It just cycles through dns records when responding and returns dns records with a set propability that corresponds to the weighting. My DNS server does not support this, and my requirements are not that precise. If it doesnt weight perfectly its okay, but it should go into the right direction. I think using the TTL field could be a more elegant and easier solution - and it deosnt require a dns server that controls this dynamically, which saves resources - which is in my opinion the whole point of dns load balancing vs hardware load balancers. My question now is... are there any best prectices / methos / rules of thumb to weight round robin distribution using the TTL attribute of DNS records? Edit: The system is a forward proxy server system. The amount of Bandwidth (not requests) exceeds what one single server with ethernet can handle. So I need a balancing solution that distributes the bandwidth to several servers. Are there any alternative methods than using DNS? Of course I can use a load balancer with fibre channel etc, but the costs are rediciulous and it also increases only the width of the bottleneck and does not eliminate it. The only thing i can think of are anycast (is it anycast or multicast?) ip addresses, but I don't have the means to set up such a system.

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• For Australian audiences, would an uncached .com.au domain resolve faster than an uncached .com?

  - by thomasrutter

  Is there any speed benefit to using a .com.au domain rather than a .com if your customers, hosting and DNS services are in Australia, specifically in the worst typical case (domain is not cached in any local DNS relay for customer)? Assuming that both domains pointed to the same nameservers in the end. I know this is mostly academic because we are talking about a DNS lookup that would take at most a few hundred milliseconds and would only be relevant once at the beginning of a session. I just was curious. I know that an uncached .com lookup will involve consulting at least one ?.gtld-servers.net. server and an uncached .com.au will involve consulting at least one ?.au. server. Now, what I guess I'd need to know is Are the various ?.gtld-servers.net. servers using anycast technology that would have local fully authoritative nodes in Australia, making them just as fast to Australians as ?.au. and avoiding a 200ms+ overseas latency, or are some or all of them hosted only in the US or in the northern hemisphere?

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