Hi Ajay,

 

As far as I understand this issue (I cannot give you an exact, perfect
explanation), a copy of the update ist stored in memory before all the
policies are applied. The BGP Scanner then takes the prefixes from that
location and applies all the necessary policies and places it to the BGP
table.

This can be interesting if you do a lot of inbound stuff to your prefixes
(for example prefix filteringÂ…) so then with the command:

 

sh ip bgp neighbors <neighbor-address> received-routes

 

You can check what came in before the prefix went through the whole process.
But as mentioned in your post, this needs a lot of memory, because the
router has to store all these prefixes in memory. Imagine what happens if
someone sends the whole internet prefixesÂ….

 

Roger

 

Von: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Im Auftrag von Ajay Chenampara
Gesendet: Freitag, 4. April 2008 23:04
An: ZEESHAN SANAULLAH; [EMAIL PROTECTED]; [email protected]
Betreff: [OSL | CCIE_RS] BGP soft reconfiguration

 

"The obvious drawback to using inbound soft reconfiguration is that memory
is required to store the updates. If the neighbor is advertising a large
number of routes, or if updates from many neighbors are being stored, the
impact on the local router's memory can be significant." - Jeff Doyle Vol 2
......
I hope you can help me understand this. Does the above statement mean that :
    1. Current inbound policies are still applied to incoming updates and a
copy of the update (even if rejected by current policy) is maintained in the
BGP table but not used for routing decisions.
    2. After the clear ip bgp neighbor <ip> soft in is executed, the new
inbound policy is applied to the currently stored updates.
    3. Future updates use the new inbound policy but a copy is still
maintained because the neighbor <> bgp soft-reconfiguration inbound is
applied to the bgp process.
    

Also, I read that IOS 12.1 and greater does not need the "neighbor <> bgp
soft-reconfiguration inbound" and support dynamic inbound reconfiguration.
So IOS 12.1 and greater will cause the router to store a copy of the updates
no matter what.

Comments?

  

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