passive interface combined with network ( for EIGRP) and with network .. area ( for OSPF) allow to advertise the IP subnet associated to the involved interface as an internal route ( for EIGRP and for OSPF) without building neighborships on it.
A typical example is a campus network with 20 client vlans - 20 IP subnets served by two multilayer switches SW1 and SW2.
The IP subnets associated to these client vlans have to be advertised in the IGP in order to allow return traffic to client PCs from everywhere.
If we simply use the network ( for EIGRP) or network area command ( for OSPF) we achieve the advertisement but the price to pay is that SW1 and SW2 become neighbors in all 20 client Vlans. This is clearly a waste of resources as SW1 and SW2 are already interconnected by other means.
An alternative could be the use of redistribute connected eventually with a route filter implemented with a route-map.
However, redistributing connected creates external routes and this is specially important with OSPF: external routes are placed into LSA 5 type 2 or type 1 and they cannot be filtered at area boundary.
[toc:faq]The ProblemOn traditional switches whenever we have a trunk
interface we use the VLAN tag to demultiplex the VLANs. The switch needs
to determine which MAC Address table to look in for a forwarding
decision. To do this we require the switch to do...
[toc:faq]Introduction:Netdr is a tool available on a RSP720, Sup720 or
Sup32 that allows one to capture packets on the RP or SP inband. The
netdr command can be used to capture both Tx and Rx packets in the
software switching path. This is not a substitut...
IntroductionOSPF, being a link-state protocol, allows for every router
in the network to know of every link and OSPF speaker in the entire
network. From this picture each router independently runs the Shortest
Path First (SPF) algorithm to determine the b...