Technical Tip: BGP prefix compared to static locally originated route weight

mkatary · ‎01-15-2022

Description

This article describes the BGP behavior in case the BGP prefix being compared to a locally originated static route.

Scope

In case prefix via BGP is learnt and there is a static route with higher AD to act as backup in case of BGP is down.

BGP route will not be installed in routing table if this static route is redistributed into BGP as locally originated weight is 32768 and learnt prefix default weight is 0 (none).

Solution

Set higher weight for incomplete BGP prefix.

FGT50E-2 # show router static

# config router stati

edit 4

set dst 10.116.0.1 255.255.255.255

set distance 50

set device "50E_200E"

FGT50E-2 # get router info bgp network 10.116.0.1

BGP routing table entry for 10.116.0.1/32

Paths: (2 available, best #2, table Default-IP-Routing-Table)

Advertised to non peer-group peers:

10.109.17.3

65200

10.109.17.3 from 10.109.17.3 (10.109.17.3)

Origin incomplete metric 0, localpref 100, valid, external

Last update: Thu Jan 13 11:39:07 2022

Local

0.0.0.0 from 0.0.0.0 (10.109.16.105)

Origin incomplete, localpref 100, weight 32768, valid, sourced, best

Last update: Thu Jan 13 11:38:44 2022

FGT50E-2 # get router info routing-table all

Routing table for VRF=0

Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP

O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default

S* 0.0.0.0/0 [10/0] via 10.109.31.254, wan1

C 10.109.16.0/20 is directly connected, wan1

S 10.116.0.0/20 [10/0] is directly connected, 50E_200E

S 10.116.0.1/32 [50/0] is directly connected, 50E_200E

C 10.132.0.0/20 is directly connected, lan

C 169.254.1.0/24 is directly connected, fortilink

In this case it is necessary to set a higher weight for the BGP prefix as to be preferred over the static when BGP is restored.

# config router prefix-lis

edit "acl-weight"

config rule

edit 1

set prefix 10.116.0.1/32

unset ge

unset le

# config router route-ma

edit "weight-in"

config rule

edit 1

set match-ip-address "acl-weight"

set set-weight 40000

# config router bg

# config neighbo

edit "10.109.17.3"

set route-map-in "weight-in"

end

Check now, it is now possible to see the new route preferred due to higher weight.