11-17-2005 09:13 AM - edited 03-03-2019 11:00 AM
Hi,
Can prefix-list ISP-IN deny 128.0.0.0/2 ge 17 actually block the entire Class B addresses when applied on a BGP neighbor..
11-17-2005 10:48 AM
No. If you want to filter the 128.0.0.0/16 net, then the following prefix list is what you need.
ip prefix-list ISP-IN deny 128.0.0.0/16 le 17
This prefix list precisely matches the class B net and subnets of same class B aren't matched.
HTH,
Sundar
11-17-2005 11:08 AM
Hi,
I shall be more specific in my query now.
Lets say I want to deny the entire class B network i.e. 128.0.0.0 -191.255.255.255 will the ip prefix-list ISP-IN deny 128.0.0.0/2 ge 17 work ??
Tx/Rgs
K Gupta
11-17-2005 12:36 PM
The answer is yes, assuming you want to accept the /16 and reject any more specific prefixes.
Hope this helps,
11-21-2005 10:59 AM
Hi,
I tried to figure the prefix-list out but somehow not able to understand how 128.0.0.0/2 can cover till the 191.0.0.0 network ..Gr8 help if u help me uncover the trick
regs
Kas
11-21-2005 01:35 PM
128.0.0.0/2 means that the first and second bits have to be 1 and 0 respectively. Anything in the range of 128.0.0.0 (0x10000000) to 191.255.255.255 ( 0xbfffffff) will match.
let me know if it helps,
11-21-2005 01:36 PM
Let's take a look.
128.0.0.0/2 transalates to binary value of 10000000 and the subnet mask of 2 bits transalates to 11000000.
The first 2 bits have to be always 10 (or 128 only)and cannot change and the 6 later bits (don't care bits) can be 1 or 0. If all 6 later bits are on, i.e 10111111 - IP is 191. Hence, all IP addresses in the range of 128-191 falls within this range.
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: