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BGP configuration - direction

TRACY HARTMANN
Beginner
Beginner

router bgp XXXXX
bgp log-neighbor-changes
network X.X.X.X mask 255.255.255.0
network c.c.c.c mask 255.255.255.0
neighbor ab.ab.ab.ab remote-as 7029
neighbor ab.ab.ab.ab update-source TenGigabitEthernet0/0/1
neighbor ab.ab.ab.ab soft-reconfiguration inbound
neighbor ab.ab.ab.ab prefix-list M-BGP-OUT out

 

and

router bgp XXXXX
bgp log-neighbor-changes
bgp bestpath as-path multipath-relax
network X.X.X.X mask 255.255.255.0
network c.c.c.cmask 255.255.255.0
neighbor cc.cc.cc.cc remote-as 7018
neighbor cc.cc.cc.cc ebgp-multihop 3
neighbor cc.cc.cc.cc update-source TenGigabitEthernet0/0/1
neighbor cc.cc.cc.cc soft-reconfiguration inbound
neighbor ab.ab.ab.ab remote-as 7029
neighbor ab.ab.ab.ab update-source TenGigabitEthernet0/0/0
neighbor ab.ab.ab.ab soft-reconfiguration inbound
neighbor ab.ab.ab.ab prefix-list WINDSTREAM-BGP-OUT out
Maximum-path 2  

 

I have two routers running BGP and they back each other up if the BGP goes down on one of the routers.  I have worked this in the past and it works well.  However I was wondering if the config on the one router is setup correctly since it does not have some of the config as the 1st one.

 

 

 

 

 

11 Replies 11

balaji.bandi
VIP Community Legend VIP Community Legend
VIP Community Legend

I only see the different another AS peer and some additional tweakings?

do you have really have to peer with 7018 neighbour- check this.

 

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TRACY HARTMANN
Beginner
Beginner

This is the biggest command I am concerned with

 

bgp bestpath as-path multipath-relax

we do not have any visibility how many paths you have, so we need some more information :

 

refer below document more clarity about your concern.

 

https://ccieblog.co.uk/bgp/bgp-unequal-load-cost-sharing

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MHM Cisco World
Advisor
Advisor

if one peer is multi hop how the other peer config without it ?

That was my concern is I see one as mulitpath and not the other I would think they should both be configured this way.   there are only two paths one from each router.

Hello

your first rtr has only 1peering the second rtr has two peerings as such ecmp has been enabled on those two peerings to accommodate same as-path prefix length 


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Paul

Both routers only have 1 physical ISP connection out.   In the BGP configuration on the 1 router it has two remote-as #'s it is to the ISP on the circuit that is connected and then the 2nd ISP router's AS #

 

then on the 2nd router in the BGP area it only references the ISP AS# of the circuit that is attached to the router.  So what I am wondering is if I need that other AS# referenced so both routers reference each other?

 

Again if I do add that 2nd AS# on the 2 router do I also add the Max-path 2 and BGP Bestpath command.

 

Just making sure I have the configurations correct for both BGP routers that attach to different ISPs.

Hello Tracy

Would it possible to attach a simple topology diagram please, it would help in visualizing the setup?


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Paul

Hello Tracy

Both rtrs have a peering to ASN 7029 with rtr2 also peering with ASN 7018 suggesting ecmp multi path but you ha e only one physical connection.

Can you confirm if both of these rtrs reside in the same local AS if so it would be recommended to have a ibgp peering between them or is it that they already have a igp connection doing this?


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This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

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Paul

Hello @TRACY HARTMANN ,

>> Both routers only have 1 physical ISP connection out. In the BGP configuration on the 1 router it has two remote-as #'s it is to the ISP on the circuit that is connected and then the 2nd ISP router's AS #

 

At this point I would start from the basics

Check with

show ip bgp summary

 

if both eBGP peers are in established state ( you should see a number of prefixes in the righmost column).

 

The second consideration is that if the router where the single WAN link terminates fails both eBGP sessions will be turned down. So there is no real redundancy.

The third consideration is that being user traffic IP based the router on the path is the one that decides where traffic is sent.

 

Even if your router would like to send traffic to not direclty connected eBGP peer it is actually sending it to the directly connected eBGP peer that examines the packet and can take a different routing decision.

 

In short, there is no real redundancy and the load balancing in upstream direction is not guaranteed, rather it is more apparent then real.

 

Hope to help

Giuseppe

 

MHM Cisco World
Advisor
Advisor

ghghghg.png

If I am right this is your design, 
Edge router have direct connect to ISP router and you want to interconnect the Both edge router?
the answer is Yes it better to connect both edge router because if the Edge-ISP link is failed then the Edge router can redirect traffic to other edge router.

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