distribute list

[carl_townshend]

what do we use these for, are they to stop routes being injected into a routing protocol ? can anyone give me an example ?

[Edison Ortiz]

RouterA's networks

192.168.1.0 /24

192.168.2.0 /24

192.168.3.0 /24

Router B's networks

192.168.4.0 /24

192.168.5.0 /24

192.168.6.0 /24

Both routers are running EIGRP and you want to block

192.168.1.0 /24 from being advertised from RouterA to RouterB.

On RouterA you type the following:

access-list 5 permit 192.168.2.0 0.0.0.255

access-list 5 permit 192.168.3.0 0.0.0.255

router eigrp 1

network 192.168.0.0 0.0.255.255

distribute-list 5 out

no auto-summary.

[carl_townshend]

in which case would you just not advertise 192.168.1.0 in the first place ?

[Edison Ortiz]

The access-list can be modified in different ways to block 192.168.1.0 / 24 from being advertised. Here is another approach:

On RouterA you type the following:

access-list 5 deny 192.168.1.0 0.0.0.255

access-list 5 permit any

router eigrp 1

network 192.168.0.0 0.0.255.255

distribute-list 5 out

no auto-summary.

[gpulos]

a 'distribute-list' is used to define what specific routing updates are sent/received by a routing protocol such as eigrp or ospf.

for example, if you have a requirement that your ospf network does not receive certain routing updates, you can create a 'distribute-list' in router configuration mode.

see these links for more info:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fiprrp_r/ind_r/1rfindp1.htm#wp1017725

http://www.cisco.com/cgi-bin/Support/Cmdlookup/ios-command-lookup.pl?type=reference&query=distribute-list&paging=25&counter=0&release=122&sa=Submit

[m-haddad]

What other said is correct. It is for route filtering. You can use prefix list or access list. Prefix list allows for more options for the route manipulation. Moreover, in prefix list you can add modify individual lines without the need to remove and recreate ACLs.

Hope this helps,