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  1. #1
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    BGP Full vs Partial

    Hello All

    I am looking to deploy BGP for ISP multihoming and shorter hop path to customers, however i am confused whether i need to store the full table or if i can get away with a partial table? I was told that i could use a partial table, however i don't understand how as i don't know what you would filter on in a web hosting environment?

    the way i understand partial updates is that you filter on your remote sites subnets!

    Thanks for any help in advanced!

    James

  2. #2
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    James:

    Just ask the carriers you are going to be peering with to send you carrier routes and your done.
    Lee Evans, Owner/Operator
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  3. #3
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    It depends on your situation but partial routes is just fine most of the time.

  4. #4
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    how large is the "carrier routes" table? do you know by any chance if level 3 offers just sending carrier routes?

  5. #5
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    you can start with partial routes it work fine. But i think it will be better if you decide on your own, what type of situation you have it will be better

  6. #6
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    Quote Originally Posted by inspired05 View Post
    how large is the "carrier routes" table? do you know by any chance if level 3 offers just sending carrier routes?
    I don't know how large the "carrier routes" are for a particular provider because I receive full Internet routes from all carriers the current Internet Routing table stands @ about 339,000 routes all of my routers have at least 512MB of memory and routing table probably uses less than half. I guess it depends on how many providers you are going to be peering with for BGP?
    Lee Evans, Owner/Operator
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  7. #7
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    The Level3 table is about 84,000 routes announced over IPv4 & 649 on IPv6.

    But yea, it completely depends moreso on your situation then anything else. Are your target customers directly connected to the carriers you're looking to peer with? if so then yea, just get those individual carrier routes. The drawback to not running full from each carrier is your router can't perform best path selection as well. If you have a route from one carrier's partial and not from another then you've only got one route to that destination.

    Just remember if you take carrier routes only, you can only get to the destinations connected to that carrier directly.

    As Lee indicated, we're seeing about ~344,000 active paths from all our peers on IPv4 and about 4461 active IPv6 paths.

    You'll need at minimum 512MB in your router ( preferably more for future growth and other services )

  8. #8
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    sorry to be dumb but by using level 3 carrier routes am i right in saying i will only get shortest path to level 3 customers and nothing from the various uk ADSL ISP's? also is it common to run HSRP on the bgp routers internal interfaces connected to the firewall? I was just woundering how the firewall would know where to send data in the situation where one of the BGP routers died?
    Thanks

  9. #9
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    Quote Originally Posted by inspired05 View Post
    sorry to be dumb but by using level 3 carrier routes am i right in saying i will only get shortest path to level 3 customers and nothing from the various uk ADSL ISP's? also is it common to run HSRP on the bgp routers internal interfaces connected to the firewall? I was just woundering how the firewall would know where to send data in the situation where one of the BGP routers died?
    Thanks
    You would get the routes of anyone connected directly to Level3 but nothing else.

    We run BGP/OSPF mesh / BGP route server behind the edge to keep everything redundant, you could run HSRP if your don't want to run BGP internally. However based on this thread, you should really hire a network engineer/consultant than try and build your network from WHT suggestions/examples

  10. #10
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    ispired05:

    (1) BGP implies that you are multi-homing between level3 and some other ISP. Whichever of the two provides the shortest route to a particular part of the Internet will be the desired path.

    (2) When running HSRP you will have an IP address i.e.
    Router 1 will be 192.168.1.1 Router 2 will be 192.168.1.2
    your HSRP virtual IP address will be 192.168.1.3 Your firewall will point to the virtual.

    PS: I agree with the above poster.
    Lee Evans, Owner/Operator
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  11. #11
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    Quote Originally Posted by inspired05 View Post
    however i am confused whether i need to store the full table or if i can get away with a partial table
    Do you want access from the entire internet or only select ASNs ?

    Partial can be used to improve routes to certain destinations, but to be globally visible you'll still need at least 1 full table.
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  12. #12
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    Quote Originally Posted by inspired05 View Post
    sorry to be dumb but by using level 3 carrier routes am i right in saying i will only get shortest path to level 3 customers and nothing from the various uk ADSL ISP's? also is it common to run HSRP on the bgp routers internal interfaces connected to the firewall? I was just woundering how the firewall would know where to send data in the situation where one of the BGP routers died?
    Thanks
    Partial routes are normally used in conjunction with default route(s). Presumably you have 2+ carriers (if you just have 1, just take a default route and get on with your life). You could take both carriers' partial route tables and a default route for both. Subject to some finer points, this would essentially ensure that your outbound traffic destined to an address on either carrier went with that particular carrier, while other outbound traffic would go out one of the default routes, perhaps even out of both if your routers supported it and were configured appropriately.

    There are lots of reasons why that is not ideal. Other routers are going to make their next-hop decision based on complete tables in most cases, so you're going to have a different return path in most cases. That's going to happen in some cases no matter what you do, but you can imagine the annoying issues that would happen if you're consistently making route decisions different than the rest of the routers in the world.

    I would only ever take partial routes from a carrier if I was asking them to suppress announcement of my own prefixes to their peers, etc. At that point, it is no longer a usable backup connection. I'd do this when I wanted to save money routing a given (crappy) carrier's traffic over more expensive bandwidth, but I want to ensure that no one off their network ever perceives their poor performance as mine.

    If you're just getting started and you need the diversity of two carriers, get gear that can handle it and take full routes. If you're just getting started and you just need a backup, take default routes from each and pick one as primary. If you're just getting started and you're somewhere in between those two extremes, you probably ought to follow the widespread advice in this thread and get some good help

  13. #13
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    I use both full and partial routes and it depends on a number of factors. If you know you can take full routes then there isn't any reason not to do it. However, many good pieces of hardware can not handle full routes. In this situation, you need to create a filter and set a default route. What happens is your router takes in the routes within your limits and directs traffic. Any route that does not fit your guidelines gets dumped out your default route. Heres how it looks in Cisco filtering out anything less than a /22 and some other networks that shouldn't be there in the first place. Change ASN1234 and 172.16.0.1 / 192.168.0.1

    Code:
    router bgp ASN1234
    neighbor 192.168.0.1 prefix-list WORLD in
    neighbor 172.16.0.1 prefix-list WORLD in
    
    ip route 0.0.0.0 0.0.0.0 192.168.0.1
    
    ip prefix-list WORLD seq 10 deny 1.0.0.0/8 le 32
    ip prefix-list WORLD seq 15 deny 10.0.0.0/8 le 32
    ip prefix-list WORLD seq 30 deny 127.0.0.0/8 le 32
    ip prefix-list WORLD seq 35 deny 128.0.0.0/16 le 32
    ip prefix-list WORLD seq 40 deny 191.255.0.0/16 le 32
    ip prefix-list WORLD seq 45 deny 169.254.0.0/16 le 32
    ip prefix-list WORLD seq 50 deny 172.16.0.0/12 le 32
    ip prefix-list WORLD seq 60 deny 192.168.0.0/16 le 32
    ip prefix-list WORLD seq 65 deny 224.0.0.0/3 le 32
    ip prefix-list WORLD seq 301 permit 0.0.0.0/0 ge 8 le 22
    ip prefix-list WORLD seq 302 deny 0.0.0.0/0 le 32
    Last edited by RSanders; 02-14-2011 at 11:28 AM. Reason: added line
    managedway
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  14. #14
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    Quote Originally Posted by inspired05 View Post
    Hello All

    I am looking to deploy BGP for ISP multihoming and shorter hop path to customers, however i am confused whether i need to store the full table or if i can get away with a partial table? I was told that i could use a partial table, however i don't understand how as i don't know what you would filter on in a web hosting environment?

    the way i understand partial updates is that you filter on your remote sites subnets!

    Thanks for any help in advanced!

    James
    BGP is depends on AS shortest path. That is not mean that is the shortest hop of each routing path.

  15. #15
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    Quote Originally Posted by RSanders View Post
    I use both full and partial routes and it depends on a number of factors. If you know you can take full routes then there isn't any reason not to do it. However, many good pieces of hardware can not handle full routes. In this situation, you need to create a filter and set a default route. What happens is your router takes in the routes within your limits and directs traffic. Any route that does not fit your guidelines gets dumped out your default route. Heres how it looks in Cisco filtering out anything less than a /22 and some other networks that shouldn't be there in the first place. Change ASN1234 and 172.16.0.1 / 192.168.0.1

    Code:
    router bgp ASN1234
    neighbor 192.168.0.1 prefix-list WORLD in
    neighbor 172.16.0.1 prefix-list WORLD in
    
    ip route 0.0.0.0 0.0.0.0 192.168.0.1
    
    ip prefix-list WORLD seq 10 deny 1.0.0.0/8 le 32
    ip prefix-list WORLD seq 15 deny 10.0.0.0/8 le 32
    ip prefix-list WORLD seq 30 deny 127.0.0.0/8 le 32
    ip prefix-list WORLD seq 35 deny 128.0.0.0/16 le 32
    ip prefix-list WORLD seq 40 deny 191.255.0.0/16 le 32
    ip prefix-list WORLD seq 45 deny 169.254.0.0/16 le 32
    ip prefix-list WORLD seq 50 deny 172.16.0.0/12 le 32
    ip prefix-list WORLD seq 60 deny 192.168.0.0/16 le 32
    ip prefix-list WORLD seq 65 deny 224.0.0.0/3 le 32
    ip prefix-list WORLD seq 301 permit 0.0.0.0/0 ge 8 le 22
    ip prefix-list WORLD seq 302 deny 0.0.0.0/0 le 32
    Thats a horrible way to filter. Its much easier to just use a route map. Ask your providers to _also_ send you default routes + full routes or default + partial.


    ip as-path access-list 10 seq 594 deny _4648_
    ip as-path access-list 10 seq 596 deny _3243_
    ip as-path access-list 10 seq 597 deny _8402_
    ip as-path access-list 10 seq 690 permit .*

    ip as-path access-list 15 seq 100 permit _1112$
    ip as-path access-list 15 seq 105 permit _174_
    ip as-path access-list 15 seq 110 permit _4439_
    ip as-path access-list 15 seq 200 deny .*

    router bgp ASN1234
    neighbor 192.168.0.1 route-map AS1111-in in
    neighbor 172.16.0.1 route-map AS1112-in in

    !
    route-map AS1111-in permit 10
    match as-path 10
    !
    route-map AS1112-in permit 10
    match as-path 15
    set local-preference 110
    !
    So this obviously isn't 100% correct but you'll get the idea. with route maps you can control everything based on the order of your route-maps. If you are getting two partial routes + default simply elevate the preference for the as-paths that you want preferred over the other network, create a match statement to match default route and set one med lower than the other to direct/preferrer your default route. NEVER EVER EVER EVER EVER EVER EVER create a static default route. _ever_ever_ever_ever. Or else if that default route/neighbor goes down guess what? You are out of luck unless you have a higher preference set for a specific AS number that doesn't hit the default route. If you set your default route higher pref than a elevated as-set than the default route wins and bypasses your little local pref/route maps.

    this syntax is based off foundry/brocade but cisco is close enough.

  16. #16
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    Thats a horrible way to filter. Its much easier to just use a route map. Ask your providers to _also_ send you default routes + full routes or default + partial.
    You should read your example over again. Your list only filters out specific ASN (which we have in our route maps as well) where as mine filters out based on announcement size (i.e. smaller than a /22) which are two different things. We actually use both methods, but the first answers the OP question and the second does traffic shaping.

    You are right about having your provider send you partial routes. That will make this a moot point, but I prefer to control that in house.
    managedway
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  17. #17
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    Quote Originally Posted by RSanders View Post
    You should read your example over again. Your list only filters out specific ASN (which we have in our route maps as well) where as mine filters out based on announcement size (i.e. smaller than a /22) which are two different things. We actually use both methods, but the first answers the OP question and the second does traffic shaping.

    You are right about having your provider send you partial routes. That will make this a moot point, but I prefer to control that in house.
    nevermind, i missed something.

  18. #18
    Zak (Spudstr) just sent his full route table to one of my Vyatta routers. Was ~360,000 routes.

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  19. #19
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    Wondering why you are getting 12K more routes than the rest of us?
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  21. #21
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    Quote Originally Posted by Jay Suds View Post
    Wondering why you are getting 12K more routes than the rest of us?
    More/less aggregation depending on the upstreams and peers.
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