BGP Prepend Issue

[santosh kumar]

Hi,

I have 2 locations with same ISP provider and having advertised our own Public pool in both the location. We configured BGP prepend and its working fine from last 5 months.

Suddenly its observed that from few internet providers the trace is going to the second location which is causing an issue. 

Can someone guide to fix the issue.

Regards,

Santosh

[paul driver]

Hello

---

@santosh kumar wrote:

Hi,

I have 2 locations with same ISP provider and having advertised our own Public pool in both the location. We configured BGP prepend and its working fine from last 5 months.

Suddenly its observed that from few internet providers the trace is going to the second location which is causing an issue. 

Can someone guide to fix the issue.

Regards,

Santosh

---

Although it might work for you immediate ISP you may well experience this as you dont have any control on what the other isp's are doing regards re-advertising your prefix or any summary's of it.

On a side not -Can you post your pre-pending configuration.

[santosh kumar]

Hi Paul,
Please find config below..

interface GigabitEthernet0/0/0
description "ISP-WAN"
ip address x.x.220.202 255.255.255.248
load-interval 30
no negotiation auto

router bgp XXXX
bgp log-neighbor-changes

neighbor x.x.220.201 remote-as XXX
neighbor x.x.220.201 description ISP
neighbor x.x.220.201 password 7 AAAAAAAAAAAAAAAAAAA
!
address-family ipv4
redistribute connected
redistribute static route-map rm-static-to-bgp
neighbor x.x.220.201 activate
neighbor x.x.220.201 send-community
neighbor x.x.220.201 soft-reconfiguration inbound
neighbor x.x.220.201 route-map rm-ISP-in in
neighbor x.x.220.201 route-map rm-ISP-out out
exit-address-family
!
ip forward-protocol nd

ip prefix-list pl-ISP-wan seq 10 permit x.x..220.200/29
!
ip prefix-list pl-default-route seq 10 permit 0.0.0.0/0
!
ip prefix-list pl-AAAA-block description opsramp-bgp-block
ip prefix-list pl-AAAA-block seq 10 permit Y.Y.248.0/24
ip sla enable reaction-alerts
logging trap debugging
logging facility local5
cdp run
!
route-map rm-ISP-in permit 10
match ip address prefix-list pl-default-route
!
route-map rm-ISP-in deny 900
!
route-map rm-connected-to-bgp permit 10
match ip address prefix-list pl-ISP-wan
!
route-map rm-connected-to-bgp deny 999
!
route-map rm-static-to-bgp permit 10
match ip address match ip address prefix-list pl-AAAA-block
set origin igp
!
route-map rm-static-to-bgp deny 900
!
route-map rm-ISP-out permit 10
match ip address prefix-list pl-AAAA-block
set as-path prepend 1111 1111 1111 1111
!
route-map rm-ISP-out deny 900
!

[paul driver]

Hello

A couple of things....

Soft inbound reconfiguration is very resource intensive and isn't required with the bgp route refresh feature, I doesn't mater too much because you are only excepting a default route  but i thought it was worth mentioning.

Also I see you are adverting only one prefix and setting its origin to igp,  As stated its possible the upstream isp's could lose this origin upon re-advertisement or also lose your pe-prending upon using their own routing bpp polices ?

Alternative to your outbound RM , you could use an As-Path acl so just to advertise locally originated routes, This will negate any chance of your rtr becoming a transit path between either isp.

ip as-path access-list 10 permit ^$

router bgp xx
no neighbor x.x.220.201 route-map rm-ISP-out out
neighbor x.isp 1.x.x filter-list 10 out

neighbor x.isp 2.x.x filter-list 10 out

[santosh kumar]

Hi Paul,

Thank you for the update. I will check the configuration.

[dbeattie]

Does your ISP have a looking glass server that you can get onto? it would be good to see the full BGP table entries for your prefixes, including any that are not selected as best.

Hope this helps,

Dave

[santosh kumar]

Thank you and Let me check Dave.