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Community Member

BGP route-map

Hi, I have configured the root map as below to preffer my ISPB over ISPA for only one prefix for outbound traffic,but some how all my inbound traffic start comming through ISPB as well for the rest of 10 prefixes., any advice on my config please,

Router bgp 10

neighbor 43.252.0.6 remote-as 3484

neighbor 19.50.16.5 remote-as 3350

neighbor 43.252.0.6 route-map WT in

network 43.252.12.0 mask 255.255.255.0

network 43.252.80.0 mask 255.255.252.0

network 43.252.130.0 mask 255.255.252.0

ip route 43.252.12.0 255.255.255.0 Null0 250

route-map WT permit 10

match ip address name WT

set weight 65534

!

route-map WT permit 20

ip access-list standard WT

permit 43.252.12.0 0.0.0.255

7200-CC-1#sh ip route list WT

D 43.252.12.0/24

[90/3072] via 43.252.1.2, 00:36:07, GigabitEthernet0/3

11 REPLIES
Community Member

Re: BGP route-map

HI,

Can you send the running-config of the router so that it can be clear that how u r giving preference to ispA over ISrPB.

And if i am not wrng u wanna to send a particular subnet through ISPB.

also let me know that u wanna failover between ISP-A and ISP-B. Right ?

Thanks and Regards

Mahi

Community Member

Re: BGP route-map

hi,

I have not got full config ,cos I am not in office , but config above is for router A which have 2 ebgp peers. peer1 with my other router B (43.252.0.6)with diffrent AS neighbor 43.252.0.6 remote-as 3484

, and here is ISPB connected.

2nd ebgp peer on this router is with ISPA on this router,

neighbor 19.50.16.5 remote-as 3350

I do want failover .

Regards,

Re: BGP route-map

Hi

Weight will control oubound traffic, but this does not mean that traffic inbound will return on same path.

if you want control inbound and outbound, use AS pre-pending on inbound and outbound for the specific prefix. This will also give you failover.

HTH

Sam

Community Member

Re: BGP route-map

I used weight only for one prefix,but it effect all my outbound and inboud traffic for my remainning 10 prefixes.I must admit I did not apply AS prepend outbound, but the route map above shold only effect o one prefix oubotbound .

Re: BGP route-map

I might be missing something here...you are advertising 43.252.12.0/24 and you are trying to get inbound traffic for this prefix to get in from one ISP and not the other. is this correct ?

Your route map in this case will have no effect as it will not match any prefixes received( since you are advertising them not your ISP).

to confirm that route map is not making a difference , remove it and you should see that nothing will change.

Please confirm if you need to influence prefixes you are sending or receiving.

I apologise in advance if I mis understood you.

Sam

Community Member

Re: BGP route-map

Sam,

My all traffic is going through ISPA,i would like to 43.252.12.0/24 prefix to preffer outbound and inbound through ISPB and leave remainning unchanged.

I hope it makes clear.

Re: BGP route-map

Hi

I presume ISPB=AS3350

neighbor 43.252.0.6 remote-as 3484

neighbor 19.50.16.5 remote-as 3350

neighbor 43.252.0.6 route-map PRE-AS out

route-map PRE-AS permit 10

match ip address name WT

set as-path 10

route-map PRE-AS permit 20

with above Route map, ur prefix is less desirable for ISPA and therfore traffic should come from AS 3350. this takes care of inbound traffic.

for outbound, Hmm...hard to see what can be done without having info on ur set up, topology and internal routing.

if you make a change to ISP A or B prefixes, all of your subnets will be affected the same way. so we have to find a way to influence 42.252.12.0 and only this subnet to exit thru ISP B as primary point.

How is this subnet getting routing info on ISP A or B prefixes. are u using default routes.

1-can you influence (using IGP) next hop to prefer exit point towards ISP B.

2-If you are not using default routes yet, can you advertise one to 43.252.12.0 domain only pointing to ISP A, so ISP B is always primary as it will have longest match prefixes. ISP A default route will only be used if ISP B session fails.

HTH

Sam

Community Member

Re: BGP route-map

Sam,

I am getting 0/0 from both isp.ISPA defult is *>. I will use prepend to influence the inbound, but still not sure about outbound.only 2 option I have weight and local-pref, but cant use local-pref cos i am not using ibgp.

Re: BGP route-map

Hi Mohammed

Inbound traffic will be resolved by pre-pending.

the challenge now is outbound traffic.

If both you are advertising 0/0 from both ISPs, which ever Next HOP in this case ISPA will be prefered for all traffic from all your subnets and not just the one you want.

Weight and local pref will not resolve this.We need to look at IGP.

I assume you have a HOT potato situation and BGP RID is selecting factor to best path.

Depending on which IGP you are using, you need to influence the above for ur subnet only.

are you bale to create a static route to NH ISP B link and advertise it to your subnet only and make sure it is filtered out to other ones ?

if you can achieve the above, your subnet will select ISP B as exit since BGP RID is more attractive.

HTH

Sam

Community Member

Re: BGP route-map

I am using EIGRP as IGP.so you mean I do this

ip route 43.252.12.0 255.255.255.0 ISPB's address?.

Keep in mind I am alredy using ststic route to install into bgp as bello.

ip route 43.252.12.0 255.255.255.0 null0 250

Re: BGP route-map

No,

assuming you see on ut BGP table > 0.0.0.0 pointing to 19.50.16.5

ip route 19.50.16.5 255.255.255.255 x.x.x.x

where x.x.x.x is the IP address that is NH on link where subnet 43.252.12.0 is located.

can u post more info , diagram and config. this will clarify things a bit more.

HTH

Sam

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