http://www.networkingblog.in/secondary-address-2889 Cisco Netpro Blog Wed, 23 Jun 2010 06:07:14 +0000 hourly 1 http://wordpress.org/?v=3.0 http://www.networkingblog.in/secondary-address-2889/comment-page-1#comment-2022 Kumar Mon, 15 Mar 2010 12:44:53 +0000 http://www.networkingblog.in/?p=2889#comment-2022 There is another aspect of secondary addresses which you should be aware of and which does impact using secondary addresses with routing protocols including EIGRP. The routing updates (and the EIGRP HELLO messages) have their source address as the primary address and not the secondary address. So EIGRP can not form neighbor relationships using the secondary addresses. This means that all routers on that segment must have primary addresses in the same subnet, and configure EIGRP to use both the primary address and the secondary address. If you do not do this EIGRP will not be able to form neighbor relationship and will not advertise routes. There is another aspect of secondary addresses which you should be aware of and which does impact using secondary addresses with routing protocols including EIGRP. The routing updates (and the EIGRP HELLO messages) have their source address as the primary address and not the secondary address. So EIGRP can not form neighbor relationships using the secondary addresses. This means that all routers on that segment must have primary addresses in the same subnet, and configure EIGRP to use both the primary address and the secondary address. If you do not do this EIGRP will not be able to form neighbor relationship and will not advertise routes.

]]> http://www.networkingblog.in/secondary-address-2889/comment-page-1#comment-2021 karan Mon, 15 Mar 2010 12:44:27 +0000 http://www.networkingblog.in/?p=2889#comment-2021 There are 2 disadvantages I can think of, though neither are really specific to EIGRP. 1. Traffic between the 2 subnets has to pass through the router even though they are in the same broadcast domain. This "one-armed" routing is probably not a big deal unless there is a huge amount of traffic between the subnets. 2. You can't use DHCP via ip helper addresses for PCs in the secondary subnet. The router will always use the primary subnet when it relays the DHCP request to the DHCP server. There are 2 disadvantages I can think of, though neither are really specific to EIGRP.
1. Traffic between the 2 subnets has to pass through the router even though they are in the same broadcast domain. This “one-armed” routing is probably not a big deal unless there is a huge amount of traffic between the subnets.
2. You can’t use DHCP via ip helper addresses for PCs in the secondary subnet. The router will always use the primary subnet when it relays the DHCP request to the DHCP server.

]]>