need to understand bgp

vishalpatil86 · ‎10-19-2011

hi,

following BGP config -

interface GigabitEthernet0/0

description ****Last Mile1 ABCDL****

ip address xx.xx.xx.30 255.255.255.252

duplex full

speed 100

!

interface GigabitEthernet0/1

description ****Last Mile2 EFRGH****

ip address xx.xx.xx.34 255.255.255.252

duplex full

speed 100

nterface Vlan1

ip address yy.yy.yy.225 255.255.255.240

!

router bgp 11111

no synchronization

bgp log-neighbor-changes

network yy.yy.yy.224 mask 255.255.255.240

neighbor xx.xx.xx.29 remote-as 22222

neighbor xx.xx.xx.29 route-map traffic-II in

neighbor xx.xx.xx.33 remote-as 22222

neighbor xx.xx.xx.33 route-map traffic-I out

no auto-summary

ip prefix-list POOL seq 10 permit yy.yy.yy.224/28

!

route-map traffic-I permit 10

match ip address prefix-list POOL

set as-path prepend 11111 11111 11111

!

route-map traffic-II permit 20

set local-preference 160

!

snmp-server community mlkhs RO

snmp-server community itprivate RW

snmp-server community public RO 60

snmp-server contact goagsh

i need to understand what the config is.....

pls help me on this

vishalpatil86 · ‎10-19-2011

i am having very less idea about bgp, but with the aboveh config i may come to know te concept

smitesh kharecha · ‎10-19-2011

Hi,

In layman, you are influencing the route to be prefered; from where traffic should be incoming to your network.

Regards,

Smitesh

Vaibhava Varma · ‎10-19-2011

Hi Vishal

The above BGP config is related to a dual-homed peering to an ISP 22222 whereby we want to use only1Link(ABCDL-

xx.xx.xx.29) for Active Traffic Forwarding and Receiving

To achieve the same we are maniulating the default BGP Attributes.

On peering xx.xx.xx.29 we are making the Local-Preference which is the 2nd Criterion for best path selection to be higher than the default 100 so when any traffic which has to go out from this router selects the rouets learned from this peer as next-Hop.

To achieve the above we are binding a route-map " traffic-I " to the peer xx.xx.xx.29 in inbound direction to match the entwrok and set its LP as 160

neighbor xx.xx.xx.29 route-map traffic-II in

route-map traffic-II permit 20

set local-preference 160

On peering xx.xx.xx.33 we are making the AS-Path which is the 3rd Criterion for best path selection

to be increased than default of preferring the lowest AS path for any route so that when the receiving end peer receives the route it does not select this route as compared to peer xx.xx.xx.33 and hence again all the traffic will be sent to this router via peer xx.xx.xx.29

To achieve the above we are binding a route-map " traffic-II " to the peer xx.xx.xx.33 in outbound direction to match the prefix which we are advertising via network statement via the prefix list POOL and increase its AS-length

neighbor xx.xx.xx.33 route-map traffic-I out

network yy.yy.yy.224 mask 255.255.255.240

match ip address prefix-list POOL

set as-path prepend 11111 11111 11111

ip prefix-list POOL seq 10 permit yy.yy.yy.224/28

Hoe this helps you to understand the config.

Regards

Varma