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AS Path and prepend

Wan_Whisperer
Level 1
Level 1

Please help me understand what the underlined command is dong.

ip as-path access-list 20 permit ^$

router bgp XXX
bgp log-neighbor-changes
network 151.101.XXX.0 mask 255.255.255.0
neighbor 64.94.0.XXX remote-as XXXX
neighbor 64.94.0.XXX send-community
neighbor 64.94.0.XXX soft-reconfiguration inbound
neighbor 64.94.0.XXX route-map Route_Control out

access-list 100 permit 151.101.XXX.0 0.0.0.255

route-map Route_Control permit 10
match ip **bleep** 100
!
route-map Route_Control permit 20 
match as-path 20

 

I did not include all the confige's,  Would the match as-path 20 have anything with sending prepend's?  If not with is its propose?

 

I understand using match as-path in a route-map entering my network to filter networks by AS but I do not understand it use with a route-map exiting, especially the blanket ^$ expression 

 

Thanks 

 

 

1 Accepted Solution

Accepted Solutions

^$ meaning local originate before add any AS 
^AS$ meaning match prefix start with AS, BUT you missing that the router add it AS (local) when it forward prefix and after route-map not before and hence all prefix will not advertise because all prefix not match this condition 

Screenshot (476).png