Redistribution

gojericho0

Is there a difference or reason why you would distribute with a prefix list opposed to a normal route-map pointing to an access-list?

Paul Boz

Unlike access lists, the prefix list specifies a base IP or IPv6 address and a length (the number of bits applied to the base to determine the network prefix). The tested address is matched against the prefix.

From:

http://www.juniper.net/techpubs/software/erx/junose60/swconfig-routing-vol1/html/routing-policy-config8.html

gojericho0

Paul Boz wrote:

Unlike access lists, the prefix list specifies a base IP or IPv6 address and a length (the number of bits applied to the base to determine the network prefix). The tested address is matched against the prefix.

From:

http://www.juniper.net/techpubs/software/erx/junose60/swconfig-routing-vol1/html/routing-policy-config8.html

Thanks for the link, but for some reason its not clicking.

Couldn't you do the following with a route map that points to an access list with the wildcard mask specifying the range\prefix you want?

Router(config) router ospf 1
Router(config-router)#redistribute eigrp route-map EIGRP_to_OSPF

Router(config)# route map EIGRP_to_OSPF permit 10
Router(config-route-map)# match ip address MARKETING
Router(config-route-map)# set metric 500

Router(config)# ip access-list standard MARKETING
Router(config-ext-nacl)#permit 10.180.48.0 0.0.15.255  

Wouldn't the above ACL be the same thing as using a prefix list?

Router (config)#ip prefix-list MARKETING permit 10.180.48.0/20

gojericho0

I believe I figured it out!

Router(config-ext-nacl)#permit 10.180.48.0 0.0.15.255 

Router (config)#ip prefix-list MARKETING permit 10.180.48.0/20 

If i had 10.180.52.0/30, the access list would make the route-map match, i applied it to the prefix-list instead the route would not match because it will only accept a /20 prefix

Bottom line is that prefix uses SNM and ACLs use Wild Card Masks and therefore can't distinguish classless masks after /20

Paul Boz

Yep, you got it. Sorry I wasn't more helpful earlier, I was literally on my way out the door

marlon23

The main difference is that with prefix-list you are looking for specific subnet and mask combination. With ACL you are matching everything what will match subnet and wildcard.

example:

prefix-list 10.2.3.0/24 will match only route 10.2.3.0 with mask 255.255.255.0.

ACL 10.2.3.0 0.0.0.255 will match also all subnets of this subnet, like 10.2.3.16 255.255.255.240 and so.

From practical point of view, if I match routes, I prefer prefix-list as it gives you more control and is more straight forward. ACL's are usefull for stuff like matching just EVEN subnets and so (Power of wild-card).