Is as-path prepending on an import map a tool that should be available?
I have found that on the IOS I'm testing that the prepending only applied if the same route-map is also setting local preference. Sounds like a bug to me but the bug toolkit is currently unavailable at time of posting.
The problem I wish to solve is to import overlapping routes with different route targets, with one route target's routes being preferred over another. Setting local preference would work, but I'd rather use as-path length as that is the metric we manipulate elsewhere.
If this a method that others have experience with?
Here's a test config:
ip vrf CMPA rd 1:1 import map RM-CMPA-IMPORT route-target export 1:1 route-target import 1:1 route-target import 1:2 ! ip vrf CMPB rd 1:2 import map RM-CMPB-IMPORT route-target export 1:2 route-target import 1:1 route-target import 1:2 ! router bgp 1 no synchronization bgp log-neighbor-changes no auto-summary ! address-family ipv4 vrf CMPA no synchronization network 126.96.36.199 mask 255.255.255.255 exit-address-family ! address-family ipv4 vrf CMPB no synchronization network 188.8.131.52 mask 255.255.255.255 exit-address-family ! ip extcommunity-list standard CL-CMPA permit rt 1:1 ip extcommunity-list standard CL-CMPB permit rt 1:2 !
route-map RM-CMPA-IMPORT permit 10 match extcommunity CL-CMPB set local-preference 100 set as-path prepend 65000 65000 ! route-map RM-CMPA-IMPORT permit 20 ! route-map RM-CMPB-IMPORT permit 10 match extcommunity CL-CMPA set as-path prepend 65000 65000 ! route-map RM-CMPB-IMPORT permit 20 !
interface Loopback101 ip vrf forwarding CMPA ip address 184.108.40.206 255.255.255.255 ! interface Loopback102 ip vrf forwarding CMPB ip address 220.127.116.11 255.255.255.255 !
The following outputs show that RM-CMPA-IMPORT is applying prepending, but RM-CMPB-IMPORT is not:
GBLON-SQ41-LVG01#sh ip bgp vpnv4 vrf CMPA BGP table version is 7, local router ID is 10.196.111.3 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 Route Distinguisher: 1:1 (default for vrf CMPA) *> 18.104.22.168/32 0.0.0.0 0 32768 i *> 22.214.171.124/32 0.0.0.0 0 100 32768 65000 65000 i GBLON-SQ41-LVG01#sh ip bgp vpnv4 vrf CMPB BGP table version is 7, local router ID is 10.196.111.3 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 Route Distinguisher: 1:2 (default for vrf CMPB) *> 126.96.36.199/32 0.0.0.0 0 32768 i *> 188.8.131.52/32 0.0.0.0 0 32768 i GBLON-SQ41-LVG01#
Thank you very much for recreating the issue on those platforms. Here's the output you requested:
GBLON-SQ41-LVG01#sh ip bgp vpnv4 vrf CMPB 184.108.40.206/32 BGP routing table entry for 1:2:220.127.116.11/32, version 6 Paths: (1 available, best #1, table CMPB) Not advertised to any peer Local, imported path from 1:1:18.104.22.168/32 0.0.0.0 (via CMPA) from 0.0.0.0 (10.196.111.3) Origin IGP, metric 0, localpref 100, weight 32768, valid, external, best Extended Community: RT:1:1 mpls labels in/out nolabel/nolabel(CMPB)
I opened a TAC case about this last night and they are investigating too, i'll post their findings once I know. I have also found that setting a community value also allows the prepending to apply - which obviously is a much less intrusive workaround...
In your experience is changing routing metrics on an import map not a tool that is often used? Or worse, is it not advisable/supported?
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iPXE boot in ASR9K
This document applies to NCS5500 and ASR9000 routers and has been verified as such.
traditional ECMP or equal cost multipath loadbalances traffic over a number of available paths towards a destination. When one path fails, the traffic gets r...