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Message |
Guest
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 Posted: Wed Aug 22, 2007 12:05 am Post subject: BGP Multi-Homed but traffic likes Sprint better =( |
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Hi,
I have two Cisco routes that are running BGP between Level3 and
Sprint. The BGP configs on both are pretty much the same and look
something like this:
router bgp 12345
no synchronization
bgp log-neighbor-changes
neighbor 192.168.1.1 remote-as 26383
neighbor 192.168.1.1 description iBGP link to hydra
neighbor 192.168.1.1 password 7 password
neighbor 192.168.1.1 version 4
neighbor 192.168.1.1 soft-reconfiguration inbound
neighbor 160.81.248.77 remote-as 1239
neighbor 160.81.248.77 description ebgp link to sprint
neighbor 160.81.248.77 version 4
neighbor 160.81.248.77 soft-reconfiguration inbound
no auto-summary
The other router is configured similarly. HOWEVER, if I do a show ip
bgp 209.245.19.41 (level3.net) I get:
BGP routing table entry for 209.244.0.0/14, version 891496
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Not advertised to any peer
1239 3356, (aggregated by 3356 4.69.130.12), (received & used)
160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78)
Origin IGP, metric 34, localpref 100, valid, internal, atomic-
aggregate, best
32327 7911 3356, (aggregated by 3356 4.69.130.10), (received & used)
209.183.177.125 from 209.183.177.125 (209.183.191.194)
Origin IGP, localpref 100, valid, external, atomic-aggregate
Why is Level3 prefering to go out Sprint (160.81.248.77) rather then
go out Level3 (209.183.177.125)?
I see there seems to be an extra AS hop there, but why? Shouldn't a
L3 pipe be a better route to L3? |
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Lutz Donnerhacke
Guest
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| Posted: Wed Aug 22, 2007 12:05 am Post subject: Re: BGP Multi-Homed but traffic likes Sprint better =( |
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* mhoppes@gmail.com wrote:
| Quote: | However, why is Sprint still being preferred?
|
It's called hot potato routing. Every router prefers it's own peers if all
other paramters are equal. In order to load balance your outgoing traffic,
you have to load balance the traffic in your own network to the routers.
OTOH from two routes with equal length, weight and preference the oldest onw
is prefered (assuming this one is more stable). |
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Lutz Donnerhacke
Guest
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| Posted: Wed Aug 22, 2007 12:05 am Post subject: Re: BGP Multi-Homed but traffic likes Sprint better =( |
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* mhoppes@gmail.com wrote:
| Quote: | AH! Answered my own question. My L3 pipe is going through another
carrier (I knew that), who is putting another AS number in there... so
my question, then, is.. what do I need to do to get the routes to look
even? Appending another AS number will, I believe, only affect
inbound traffic.
|
route map addmyas permit 10
set as-prepend <your as>
!
router bgp <your as>
neighbour sprint route-map addmyas in
neighbour sprint route-map addmyas out |
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Guest
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| Posted: Wed Aug 22, 2007 12:12 am Post subject: Re: BGP Multi-Homed but traffic likes Sprint better =( |
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| Quote: | I see there seems to be an extra AS hop there, but why? Shouldn't a
L3 pipe be a better route to L3?
|
AH! Answered my own question. My L3 pipe is going through another
carrier (I knew that), who is putting another AS number in there... so
my question, then, is.. what do I need to do to get the routes to look
even? Appending another AS number will, I believe, only affect
inbound traffic. |
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Guest
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| Posted: Wed Aug 22, 2007 12:46 am Post subject: Re: BGP Multi-Homed but traffic likes Sprint better =( |
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| Quote: | route map addmyas permit 10
set as-prepend <your as
!
router bgp <your as
neighbour sprint route-map addmyas in
neighbour sprint route-map addmyas out
|
Ok.. that worked as expected:
Hydra#show ip bgp 206.80.67.28
BGP routing table entry for 206.80.64.0/21, version 402504
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Flag: 0x208
Not advertised to any peer
26383 1239 3356 30512, (received & used)
160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78)
Origin IGP, metric 34, localpref 100, valid, internal, best
32327 7911 3356 30512, (received-only)
209.183.177.125 from 209.183.177.125 (209.183.191.194)
Origin IGP, localpref 100, valid, external
However, why is Sprint still being preferred? I don't want to send
ALL traffic down L3.. just traffic that is, well you know, going to
the L3 network! Even level3.net (the last entry there at 4.68.95.11)
has fewer AS hops going over L3, yet it still wants to go out Sprint!
The other odd thing is if I do a show command for L3 (4.68.95.11) on
my L3 router I get:
Hydra#show ip bgp 4.68.95.11
BGP routing table entry for 4.0.0.0/9, version 225677
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Not advertised to any peer
32327 7911 3356, (aggregated by 3356 4.69.130.10), (received-only)
209.183.177.125 from 209.183.177.125 (209.183.191.194)
Origin IGP, localpref 100, valid, external, atomic-aggregate
26383 1239 3356, (aggregated by 3356 4.69.130.12), (received & used)
160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78)
Origin IGP, metric 34, localpref 100, valid, internal, atomic-
aggregate, best
Hey it's working! But if I do it on my Sprint router I get:
medusa#show ip bgp 4.68.95.11
BGP routing table entry for 4.0.0.0/9, version 923707
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
65.165.94.77 65.173.16.33
26383 1239 3356, (aggregated by 3356 4.69.130.12)
160.81.248.77 from 160.81.248.77 (144.228.242.72)
Origin IGP, metric 34, localpref 100, valid, external, atomic-
aggregate, best
1239 3356, (aggregated by 3356 4.69.130.12), (received-only)
160.81.248.77 from 160.81.248.77 (144.228.242.72)
Origin IGP, metric 34, localpref 100, valid, external, atomic-
aggregate
eh? |
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Guest
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| Posted: Wed Aug 22, 2007 12:59 am Post subject: Re: BGP Multi-Homed but traffic likes Sprint better =( |
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On Aug 21, 3:53 pm, Lutz Donnerhacke <l...@iks-jena.de> wrote:
| Quote: | * mhop...@gmail.com wrote:
However, why is Sprint still being preferred?
It's called hot potato routing. Every router prefers it's own peers if all
other paramters are equal. In order to load balance your outgoing traffic,
you have to load balance the traffic in your own network to the routers.
OTOH from two routes with equal length, weight and preference the oldest onw
is prefered (assuming this one is more stable).
|
Ok.. I understand this.. and indeed things now look like they should
on the L3 router.. so my question would then be... what would I need
to do on the Sprint router to get it to ship traffic over to the L3
router? Ideally our L3 traffic would go there (a few subnets), but
best case would be I could get about half our traffic going out there,
and leave half on Sprint. |
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Chris
Guest
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| Posted: Wed Aug 22, 2007 1:59 am Post subject: Re: BGP Multi-Homed but traffic likes Sprint better =( |
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On Tue, 21 Aug 2007 19:46:52 -0000, mhoppes@gmail.com wrote:
| Quote: | route map addmyas permit 10
set as-prepend <your as
!
router bgp <your as
neighbour sprint route-map addmyas in
neighbour sprint route-map addmyas out
Ok.. that worked as expected:
Hydra#show ip bgp 206.80.67.28
BGP routing table entry for 206.80.64.0/21, version 402504
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Flag: 0x208
Not advertised to any peer
26383 1239 3356 30512, (received & used)
160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78)
Origin IGP, metric 34, localpref 100, valid, internal, best
32327 7911 3356 30512, (received-only)
209.183.177.125 from 209.183.177.125 (209.183.191.194)
Origin IGP, localpref 100, valid, external
However, why is Sprint still being preferred? I don't want to send
ALL traffic down L3.. just traffic that is, well you know, going to
the L3 network! Even level3.net (the last entry there at 4.68.95.11)
has fewer AS hops going over L3, yet it still wants to go out Sprint!
The other odd thing is if I do a show command for L3 (4.68.95.11) on
my L3 router I get:
Hydra#show ip bgp 4.68.95.11
BGP routing table entry for 4.0.0.0/9, version 225677
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Not advertised to any peer
32327 7911 3356, (aggregated by 3356 4.69.130.10), (received-only)
209.183.177.125 from 209.183.177.125 (209.183.191.194)
Origin IGP, localpref 100, valid, external, atomic-aggregate
26383 1239 3356, (aggregated by 3356 4.69.130.12), (received & used)
160.81.248.77 (metric 3) from 65.165.94.78 (160.81.248.78)
Origin IGP, metric 34, localpref 100, valid, internal, atomic-
aggregate, best
Hey it's working! But if I do it on my Sprint router I get:
medusa#show ip bgp 4.68.95.11
BGP routing table entry for 4.0.0.0/9, version 923707
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
65.165.94.77 65.173.16.33
26383 1239 3356, (aggregated by 3356 4.69.130.12)
160.81.248.77 from 160.81.248.77 (144.228.242.72)
Origin IGP, metric 34, localpref 100, valid, external, atomic-
aggregate, best
1239 3356, (aggregated by 3356 4.69.130.12), (received-only)
160.81.248.77 from 160.81.248.77 (144.228.242.72)
Origin IGP, metric 34, localpref 100, valid, external, atomic-
aggregate
eh?
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Match the L3 prefixes coming in via the L3 connection and then set a higher
local pref to be used within your network to prefer the L3 connection over
the Sprint connection.
Chris. |
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