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Erwin_25552's avatar
Erwin_25552
Icon for Nimbostratus rankNimbostratus
Feb 25, 2019

BGP AS-PATH prepending

We facing a challange with BGP. Situation : 2 x F5 Viprion chassis in HA setup. Each chassis has a dedicated VLAN configured to connect towards the Internet. When adding the networks to be advertised to the bgp neighbor we also use the as-local-count (1 for the active node, 4 for the standby node) as the prefered route. When the standby node becomes active we would like that the as-local-count becomes 1 and for the other node, who's become standby with an as-local-count value of 4.

 

Question, Is this possible to configure this within the ZebOS routing module? or any have an idea how to configure this? From a BGP configuration perspective on a router there is way to use a trigger were you can set the as-local-count value.

 

There is only a BGP command referance available which not showing the possiblities with the BGP.

 

Kind regards,

 

Erwin

 

application delivery
bgp
BIG-IP
TMOS
  • PeteWhite's avatar
    PeteWhite
    Icon for Employee rankEmployee
    Feb 25, 2019

    As you say, AS path prepending uses the as-local-count configuration to set the local prepending setting. As such, when you set this it is fixed on that platform so you have to use something to change it when the state changes. As with all things F5 there are multiple ways to do that - you can do it it via a script which is run by alertd ( configure user_alert.conf ), you can do it by iCall or you can create yourself a script which runs as a daemon.

     

    If it were me, i'd do it by either iCall or alertd depending on whether you have experience with iCall, tmsh scripts etc. You may find that iCall is more robust ie a periodic script which checks if device is active and sets the parameter appropriately