07-06-2010 09:56 AM - edited 03-06-2019 11:55 AM
Hi All
One quick question.. Does the subnet mask defined in a prefix list be the same as the entries on a BGP table or routing table ?
for eg if i have 10 * /32 routes on a particular router (10 different loopbacks), can i have a single prefix list with the aggregate address defined ? or do i need to have 10 different rules on the prefix list to allow the /32's ?
note - im not summarizing anywhere to convert the /32's to /24's.. they are just plain /32's on BGP table..
Thanks
Solved! Go to Solution.
07-07-2010 11:54 AM
Hello Sblavanya,
>> ip prefix-list loops seq 5 permit 10.10.10.0/24 ge 32
to allow all 10 routes to be sent to the neighbouring router ?
if they are near to each other (like 10.10.10.1, 10.10.10.2, and so on)
you can even use a more specific network like 10.10.10.0/28 as I did in my example
if they spread over the whole /24 you need to use the /24
note: without the ge 32 option the prefix list looks for the exact route 10.10.10.0/24
Hope to help
Giuseppe
07-06-2010 12:13 PM
Hi
------>One quick question.. Does the subnet mask defined in a prefix list be the same as the entries on a BGP table or routing table ?
No , It is not requried. The network in routing table & define prefix can be different.
----- >for eg if i have 10 * /32 routes on a particular router (10 different loopbacks), can i have a single prefix list with the aggregate address defined ? or do i need to have 10 different rules on the prefix list to allow the /32's ?
Yes you can have single prefix-list to define all 10 loopback address. But here you can't create single prefix with /32 for all of them. You have to create less than /32 . ( prefix-list xx seq 10 permit 10.x.x.x/24 ) or what ever you want.
In your senario if you wnat to filter teh router without aggregation the you should go with Distribution-list. Prefix list give you to play with prefix not with IP route.
Here you can get an good example.
prefix-list xx seq 10 permit 63.1.0.0/16 ge 18
The statement above allows any route announcement in the range of 63.1.0.0 - 63.1.255.255 but that announcement must have a length greater than 18 bits in the mask. This permits you to allow announcements in the range, but not an announcement equalling the entire range (/16), or even announcements of half the range (/17). Only announcments with a length "greater than or equal to" /18 will be permitted
Regards
Chetan Kumar
07-06-2010 12:29 PM
Hello Sblavanya,
another possible solution could be:
ip prefix-list loops seq 5 permit x.y.z.0/28 ge 32
Hope to help
Giuseppe
07-06-2010 03:11 PM
Hi Chetan/Guiseppe
Thanks a ton for your reply.. For eg in my case, lets assume we have the following loopbacks...
10.10.10.1/32 , 10.10.10.2/32.... -> 10.10.10.10/32
Im able to make this work by the following prefix-list:
ip prefix-list test seq xxx permit 10.10.10.1/32
ip prefix-list test seq xxx permit 10.10.10.2/32 etc
Guiseppe - as per your post can i just use one prefix-list with the following command ?
ip prefix-list loops seq 5 permit 10.10.10.0/24 ge 32
to allow all 10 routes to be sent to the neighbouring router ?
we tried---> ip prefix-list loops seq 5 permit 10.10.10.0/24 without "ge 32" and it didnt work, and now i know why
Regards
07-07-2010 08:24 AM
Hi Guiseppe..
Can you please confirm this ?
Regards
07-07-2010 11:54 AM
Hello Sblavanya,
>> ip prefix-list loops seq 5 permit 10.10.10.0/24 ge 32
to allow all 10 routes to be sent to the neighbouring router ?
if they are near to each other (like 10.10.10.1, 10.10.10.2, and so on)
you can even use a more specific network like 10.10.10.0/28 as I did in my example
if they spread over the whole /24 you need to use the /24
note: without the ge 32 option the prefix list looks for the exact route 10.10.10.0/24
Hope to help
Giuseppe
07-09-2010 12:02 PM
Thanks Guiseppe..
Ill try this and let you know if it worked good..
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