BGP issue with default routes

Freddie Eisa · ‎09-04-2011

Hello,

I'm working on a practice lab and am having the following issue

I have a customer router connected to two different ISP routers. Each ISP router must advertise a default through BGP to the customer and one of the default routes must be prefered over the other. Given if the perfered route interface is shut down the other default route is inserted into the routing table and when the perfered default route interface it turned back on that path is used again. The catch is I cant alter the customer router only the the two ISP devices. I tried doing some route maps but im lost. I have deleted all my route maps and have posted the BGP portion of the ISP routers

router bgp 300

no synchronization

bgp log-neighbor-changes

network 10.1.3.0 mask 255.255.255.0

network 183.3.3.0 mask 255.255.255.0

network 183.3.4.0 mask 255.255.255.0

redistribute static

neighbor 10.1.23.2 remote-as 200

neighbor 10.1.23.2 default-originate

neighbor 10.1.23.2 route-map route-to-customer out

no auto-summary

router bgp 100

no synchronization

bgp log-neighbor-changes

network 10.1.1.0 mask 255.255.255.0

network 191.1.1.0 mask 255.255.255.0

network 191.1.2.0 mask 255.255.255.0

redistribute static

neighbor 10.1.12.2 remote-as 200

neighbor 10.1.12.2 default-originate

no auto-summary

any direction or help would be benificial i have been on this for the last day or so.

Marwan ALshawi · ‎09-04-2011

One way to it is

Create a static default rote to null 0 in the less preferred ISP

Ip route 0.0.0.0 0.0.0.0 null0

Ip prefix-list pref1 permit 0.0.0.0/0

Route-map default

Match ip add prefix-list pref1

Route-map OUT

Match ip add prefix-list pref1

Set as-path prepend 300 300

Assuming this config in as 300 router

Router bgp 300

Redistribute static route-map default

Neighbor customerbgp ip route-map out OUT

HTH

Sent from Cisco Technical Support iPhone App

Freddie Eisa · ‎09-04-2011

Thanks for the help but the issue I face now is once i shut down the perfered default routes outgoing interface and bring it back up the alternate default route stays in the routing table. I need to be able to shut down the perfered out going interface and bring it back and able to replace the alternate route in the customer device with the perfered route.

router bgp 300

no synchronization

bgp log-neighbor-changes

network 10.1.3.0 mask 255.255.255.0

network 183.3.3.0 mask 255.255.255.0

network 183.3.4.0 mask 255.255.255.0

redistribute static route-map default

neighbor 10.1.23.2 remote-as 200

neighbor 10.1.23.2 default-originate

neighbor 10.1.23.2 route-map route out

no auto-summary

!

ip http server

ip classless

ip route 0.0.0.0 0.0.0.0 Null0

!

ip prefix-list pref1 seq 5 permit 0.0.0.0/0

route-map default permit 10

match ip address prefix-list pref1

!

route-map route permit 10

match ip address prefix-list pref1

set as-path prepend 300 300

!

line con 0

line aux 0

line vty 0 4

login

!

end

Marwan ALshawi · ‎09-04-2011

can you wait for 5 to 10 minute and see if dose show up through the preferred route when you bring it back

just to make sure the BGP route get converged

also you can check if the router is advertising the route to the customer router using the bellow command

show ip bgp neighbor 10.1.23.2 advertised-route

and see if the defaulte route got advertised or not

HTH

if helpful Rate

Marwan ALshawi · ‎09-04-2011

the other way is

remove the static to null0

remove the redistribtion and keep the AS prepend route map

add the default originate command

rest the BGP session and check the propigation of the default route

Freddie Eisa · ‎09-04-2011

Ok I will go ahead and wait then for a few minutes, quick question though is the 0.0.0.0 next hop 10.1.23.3. suppose to only show the path as 300 since I made the changes on R3.

R2#show ip bgp

BGP table version is 11, local router ID is 202.2.2.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 0.0.0.0 10.1.23.3 0 300 i

*> 10.1.12.1 0 100 i

*> 10.1.1.0/24 10.1.12.1 0 0 100 i

*> 10.1.2.0/24 0.0.0.0 0 32768 i

*> 10.1.3.0/24 10.1.23.3 0 0 300 i

*> 183.3.3.0/24 10.1.23.3 0 0 300 i

*> 183.3.4.0/24 10.1.23.3 0 0 300 i

*> 191.1.1.0/24 10.1.12.1 0 0 100 i

*> 191.1.2.0/24 10.1.12.1 0 0 100 i

*> 202.2.2.0 0.0.0.0 0 32768 i

Marwan ALshawi · ‎09-04-2011

based on the change you made it has to show only through 12.1 not 23.3

can you please post the routers config three of them with ip bgp in each of them

Freddie Eisa · ‎09-04-2011

Thank you again for all your help,

R1#show run

Building configuration...

Current configuration : 1243 bytes

!

version 12.3

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname R1

!

boot-start-marker

boot-end-marker

!

no aaa new-model

ip subnet-zero

!

ip cef

!

interface Loopback0

ip address 10.1.1.1 255.255.255.0

!

interface Loopback1

ip address 191.1.1.1 255.255.255.0

!

interface Loopback2

ip address 191.1.2.1 255.255.255.0

!

interface FastEthernet0/0

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/0

ip address 10.1.12.1 255.255.255.0

clock rate 2000000

!

interface FastEthernet0/1

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/1

no ip address

shutdown

clock rate 2000000

!

interface Serial0/2

no ip address

shutdown

clock rate 2000000

!

interface Serial0/3

no ip address

shutdown

clock rate 2000000

!

router bgp 100

no synchronization

bgp log-neighbor-changes

network 10.1.1.0 mask 255.255.255.0

network 191.1.1.0 mask 255.255.255.0

network 191.1.2.0 mask 255.255.255.0

redistribute static

neighbor 10.1.12.2 remote-as 200

neighbor 10.1.12.2 default-originate

no auto-summary

!

ip http server

ip classless

ip route 0.0.0.0 0.0.0.0 Serial0/0

!

line con 0

line aux 0

line vty 0 4

login

!

end

R2#show run

Building configuration...

*Mar 3 11:47:12.553: %SYS-5-CONFIG_I: Configured from console by console

Current configuration : 1196 bytes

!

version 12.3

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname R2

!

boot-start-marker

boot-end-marker

!

no aaa new-model

ip subnet-zero

!

ip cef

!

interface Loopback0

ip address 10.1.2.1 255.255.255.0

!

interface Loopback1

ip address 202.2.2.1 255.255.255.0

!

interface FastEthernet0/0

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/0

ip address 10.1.12.2 255.255.255.0

shutdown

clock rate 64000

!

interface FastEthernet0/1

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/1

ip address 10.1.23.2 255.255.255.0

clock rate 64000

!

interface Serial0/2

no ip address

shutdown

clock rate 2000000

!

interface Serial0/3

no ip address

shutdown

clock rate 2000000

!

router bgp 200

no synchronization

bgp log-neighbor-changes

network 10.1.2.0 mask 255.255.255.0

network 202.2.2.0

neighbor 10.1.12.1 remote-as 100

neighbor 10.1.12.1 filter-list 1 out

neighbor 10.1.23.3 remote-as 300

neighbor 10.1.23.3 filter-list 1 out

no auto-summary

!

ip http server

ip classless

!

ip as-path access-list 1 permit ^$

!

line con 0

line aux 0

line vty 0 4

login

!

end

R3#show run

Building configuration...

Current configuration : 1512 bytes

!

version 12.3

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname R3

!

boot-start-marker

boot-end-marker

!

no aaa new-model

ip subnet-zero

!

ip cef

no ip domain lookup

!

interface Loopback0

ip address 10.1.3.1 255.255.255.0

!

interface Loopback1

ip address 183.3.3.1 255.255.255.0

!

interface Loopback2

ip address 183.3.4.1 255.255.255.0

!

interface FastEthernet0/0

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/0

ip address 10.1.23.3 255.255.255.0

clock rate 2000000

!

interface FastEthernet0/1

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/1

no ip address

shutdown

clock rate 2000000

!

interface Serial0/2

no ip address

shutdown

clock rate 2000000

!

interface Serial0/3

no ip address

shutdown

clock rate 2000000

!

router bgp 300

no synchronization

bgp log-neighbor-changes

network 10.1.3.0 mask 255.255.255.0

network 183.3.3.0 mask 255.255.255.0

network 183.3.4.0 mask 255.255.255.0

redistribute static route-map default

neighbor 10.1.23.2 remote-as 200

neighbor 10.1.23.2 route-map route out

no auto-summary

!

ip http server

ip classless

ip route 0.0.0.0 0.0.0.0 Null0

!

ip prefix-list pref1 seq 5 permit 0.0.0.0/0

route-map default permit 10

match ip address prefix-list pref1

!

route-map route permit 10

match ip address prefix-list pref1

set as-path prepend 300 300

!

route-map route permit 20

!

line con 0

line aux 0

line vty 0 4

login

!

end

Marwan ALshawi · ‎09-04-2011

Hi

because i do not have now a router to test it for you bellow are two methods to configure it in R3 and both aim to make R1 default route the preferred one

method one:

router bgp 300

redistribute static route-map default

neighbor 10.1.23.2 remote-as 200

neighbor 10.1.23.2 route-map route out

no auto-summary

!

ip http server

ip classless

ip route 0.0.0.0 0.0.0.0 Null0

!

ip prefix-list pref1 seq 5 permit 0.0.0.0/0

route-map default permit 10

match ip address prefix-list pref1

!

route-map route permit 10

match ip address prefix-list pref1

set as-path prepend 300 300

!

route-map route permit 20

method 2:

router bgp 300

No redistribute static route-map default

neighbor 10.1.23.2 default-originate
neighbor 10.1.23.2 route-map route out

ip prefix-list pref1 seq 5 permit 0.0.0.0/0

route-map default permit 10

match ip address prefix-list pref1

!

route-map route permit 10

match ip address prefix-list pref1

set as-path prepend 300 300

!

route-map route permit 20

if dose not work post the following

from R2 show ip bgp when both links are up

and show ip bgp prefix-list pref1

and same when one of them is down

HTH

Freddie Eisa · ‎09-06-2011

Hello,

I tried both options and when perfered interface is brough back up it does not replace the backup route in the routing table

R2#show ip bgp

BGP table version is 32, local router ID is 202.2.2.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 0.0.0.0 10.1.12.1 0 100 i

*> 10.1.23.3 0 300 i

*> 10.1.1.0/24 10.1.12.1 0 0 100 i

*> 10.1.2.0/24 0.0.0.0 0 32768 i

*> 10.1.3.0/24 10.1.23.3 0 0 300 i

*> 183.3.3.0/24 10.1.23.3 0 0 300 i

*> 183.3.4.0/24 10.1.23.3 0 0 300 i

*> 191.1.1.0/24 10.1.12.1 0 0 100 i

*> 191.1.2.0/24 10.1.12.1 0 0 100 i

*> 202.2.2.0 0.0.0.0 0 32768 i

R3#show ip prefix-list pref1

ip prefix-list pref1: 1 entries

seq 5 permit 0.0.0.0/0

R2#show ip bgp

BGP table version is 35, local router ID is 202.2.2.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 0.0.0.0 10.1.23.3 0 300 i

*> 10.1.2.0/24 0.0.0.0 0 32768 i

*> 10.1.3.0/24 10.1.23.3 0 0 300 i

*> 183.3.3.0/24 10.1.23.3 0 0 300 i

*> 183.3.4.0/24 10.1.23.3 0 0 300 i

*> 202.2.2.0 0.0.0.0 0 32768 i

R2#

Thanks

Edison Ortiz · ‎09-06-2011

The output indicates the as-path prepend was not applied to the prefix while leaving BGP AS 300.

I tried your configuration as posted and it worked. Did you clear ip bgp * out on R3 after applying the route-map?

You should have the default route with two AS 300 listed in the path.

Freddie Eisa · ‎09-08-2011

Thank you for the help, I have it succesfully working now

Edison Ortiz · ‎09-08-2011

Glad to be of help, please mark the thread as resolved.

Marwan ALshawi · ‎09-08-2011

This is good

Pls rate the helpful posts