Table of Contents

• Routing Protocols
• Masking

Routing Protocols

We can use OSPF and IBGP for internal routing. IBGP and OSPF layer do not need to be configured explicitly; they are by default enabled on all autonomous systems.

The default behaviors are as follow:

• IBGP is configured between all routers within an autonomous system,
• OSPF is enabled on all networks that have two or more routers in them.
• Passive OSPF is enabled on all other connected networks.

Masking

We may “mask” an autonomous system from OSPF or IBGP, if we do not want the behavior. For IBGP, use Ibgp::mask method. It takes an ASN as input and will disable IBGP on that autonomous system:

ibgp.mask(151)

The above masks AS151 from IBGP, meaning the IBGP layer will not touch any router from AS151. However, in this particular example, AS151 has only one router, so it was not going to be configured by the IBGP layer anyway.

For the OSPF layer, we have a bit more customizability. To mask an entire autonomous system, use Ospf::maskAsn:

ospf.maskAsn(151)

We can also mask only a single network with Ospf::maskNetwork and Ospf::maskByName. maskNetwork call takes one parameter - the reference to the network object, and maskByName call takes two parameters, the first is the scope (i.e., ASN) of the network, and the second is the name of the network. Masking a network takes it out of the OSPF layer’s consideration. In other words, no OSPF will be enabled on any interface connected to the network, passive or active.

# mask with name
ospf.maskByName('151', 'net0')

# mask with reference
ospf.maskNetwork(as152_net)