ISP backup

Popeye_Wang · Created Oct 31, 2020 06:12:45

Hi,
By default, all the valid routes in the BGP routing table will be advertised to the BGP peers. Although We can use filter-policy or route-policy to control the advertisement of BGP routes, routes cannot be advertised conditionally by checking link status.
I think a better way is to advertise routes to both ISPs. Then, Using the local-preference and MED attributes of BGP to control traffic to leave and enter the primary ISP first.
I hope this helps.

Gustavo.HdezF · Created Oct 28, 2020 22:23:18

Hello User. we are reviewing your question and we will answer you shortly. Thanks.

DragonVN · Created Oct 28, 2020 23:25:17

Hi,

BGP advertises routes from its BGP table to external peers by default. The BGP conditional advertisement feature provides additional control of route advertisement depending on the existence of other prefixes in the BGP table. Normally, routes are propagated regardless of the existence of a different path. The BGP conditional advertisement feature uses the non-exist-map and advertise-map configuration commands to track routes by the route prefix. If a route prefix is not present in the non-exist-map command, the route specified by the advertise-map command is announced. Refer to the Configuring BGP Conditional Advertisement section of Configuring BGP for more information.

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/5816-bgpfaq-5816.html#anc19

Hope this help.

Popeye_Wang · Created Oct 31, 2020 06:12:45

Hi,
By default, all the valid routes in the BGP routing table will be advertised to the BGP peers. Although We can use filter-policy or route-policy to control the advertisement of BGP routes, routes cannot be advertised conditionally by checking link status.
I think a better way is to advertise routes to both ISPs. Then, Using the local-preference and MED attributes of BGP to control traffic to leave and enter the primary ISP first.
I hope this helps.

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