WHEN RTA GETS AN UPDATE FROM RTB WITH METRIC 50, HE CAN NOT COMPA...

200. When RTA gets an update from RTB with metric 50, he can not compare

it to 120 because RTC and RTB are in different ASs (RTA has to choose

based on some other attributes).

In order to force RTA to compare the metrics we have to add

bgp always-compare-med to RTA. This is illustrated in the configs below:

RTA#

router bgp 100

neighbor 2.2.2.1 remote-as 300

neighbor 3.3.3.3 remote-as 300

neighbor 4.4.4.3 remote-as 400

RTC#

router bgp 300

neighbor 2.2.2.2 remote-as 100

neighbor 2.2.2.2 route-map setmetricout out

neighbor 1.1.1.2 remote-as 300

route-map setmetricout permit 10

set metric 120

RTD#

neighbor 3.3.3.2 remote-as 100

neighbor 3.3.3.2 route-map setmetricout out

neighbor 1.1.1.1 remote-as 300

set metric 200

In order to have RTB included in the metric comparison, we have to

configure RTA as follows:

neighbor 2.2.21 remote-as 300

bgp always-compare-med

In this case RTA will pick RTB as the best next hop in order to reach

network 180.10.0.0.

Metric can also be set while redistributing routes into BGP, the command

is:

default-metric

number

Assume in the above example that RTB is injecting a network via static

into AS100 then the following configs:

RTB#

router bgp 400

redistribute static

default-metric 50

ip route 180.10.0.0 255.255.0.0 null 0

will cause RTB to send out 180.10.0.0 with a metric of 50.