BGP Conditional advertisements Scenario config request

Unanswered Question
Apr 17th, 2008

Hi All,


Can you please shoot me a link to an config scenario to use Conditional advertisement.

2 nternet routers, Dual ISP (rtr1-ISPA, Rtr2 -ISPB ), having our own AS# and class C N/w being advertised and EBGP with both carriers.


Wanted to run Primary/backup autofailover.


Carriers not supporting Communities.


All the config exaples iam seeing is with single router with multihomed.


Thank you in advance

MS



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Rick Morris Thu, 04/17/2008 - 12:16

Ok, you have 2 routers...


How are they connected to your ISP's?

You can run HSRP between the two routers.

Then run BGP between your routers and the ISP and weight the traffic on the second router by prepending the AS.


There are other ways but this appears to me to be one of the simplest forms to do what you want. All traffic inbound will prefer the router with the lowest AS Hops, once the peer session is dropped then the second router will assume routing. In the HSRP you would want to track the serial link.

fortis123 Thu, 04/17/2008 - 12:37

Here is the exact Scenario:


(considering 1.1.1.0/24 is our own RIPE assigned public space...)


RTR-A: 10MB Fast Ether to ISP-A


router bgp 42460

no synchronization

bgp log-neighbor-changes

network 1.1.1.0 mask 255.255.255.0

network 10.10.10.4 mask 255.255.255.224

neighbor 213.10.96.48 remote-as 21530

neighbor 213.10.96.48 ebgp-multihop 255

neighbor 213.10.96.48 remove-private-as

neighbor 213.10.96.48 soft-reconfiguration inbound

neighbor 213.10.96.48 distribute-list 15 out

neighbor 213.10.96.49 remote-as 21530

neighbor 213.10.96.49 ebgp-multihop 255

neighbor 213.10.96.49 remove-private-as

neighbor 213.10.96.49 soft-reconfiguration inbound

neighbor 213.10.96.49 distribute-list 15 out

no auto-summary

!

Fast Ether 0/1

descruption : LAN

ip address 1.1.1.2 255.255.255.0

standby 10 1.1.1.1

standby 10 preempt delay minimum 60

standby 10 priority 155

standby 10 track fast 0/0

!

distribute-list 15 : has ACL permits 1.1.1.0/24 and other /28 range to ISP-A

-----------------------------------

RTR B to ISP-B : 2MB via Serila0/0


router bgp 42460

no synchronizartion

bgp log-neighbor-changes

network 1.1.1.0 mask 255.255.255.0

neighbor 229.23.50.157 remote-as 6466

neighbor 229.23.50.157 next-hop-self

neighbor 229.23.50.157 soft-reconfiguration inbound

neighbor 229.23.50.157 route-map set-as-path out

!

ip prefix-list ISP-B seq 10 permit 1.1.1.0/24

ip prefix-list ISP-B seq 20 deny 0.0.0.0/0 le 32

!

route-map set-as-path permit 10

match ip address prefix-list ISP-B

set as-path prepend 42460 42460 42460 42460 42460

!

inter fast 0/1

description: LAN

Fast Ether 0/1

descruption : LAN

ip address 1.1.1.3 255.255.255.0

standby 10 1.1.1.1

standby 10 preempt

standby 10 priority 150

______________________________________


When I ran the test with some down time, it was observed that

1. when ISP-A link fails, it took 4-5mins for the internet to failover to ISP-B.


2. Also, when ISP-A is active, the traceroute from my PC to the public IP at this location, taking ISP-B path.


So after careful reviews, we observerved..


a) synchronization diff in both our local rtrs b) there may be IBGP required between both rtrs c) AS Path Prepend is not 100% perfect solution for primary/back up solution.


We might go with Communities or Conditional advt.

As my ISP-B does not support communities, Iam thinking of Conditional advt.


So iam looking for confg example with 2 rts, 2dual ISPs.


Thank you

MS


Also, as rtrs residing outside of firewall and not communicatiing with any internal IGP (in LAN), do I still need IBGP between these routers..? or the configs I mentioned are sufficient..?


Please suggest.

Thank you in advance

MS



fortis123 Fri, 04/18/2008 - 12:17

Hi all,



Any suggestions are welcome & appreciated for Conditional advt.


Thank you

MS

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