Does the transit network in OSPF equal MA network

[rookie R]

Hi!

There are four values of Type in LSA1 as follows.

When the Type field is type 2, it means 'Connection to a transit network', someone said if it needs to select DR\BDR, then it is a transit network. NBMA and MA network needs to select DR\BDR in OSPF, so does this meaning that the transit network is the MA network?

[Giuseppe Larosa · Accepted solution]

Hello @rookie R ,

your understanding is correct type transit network means there is at least one OSPF neighbor on the link but does not require the election of DR/BDR even if most of the times this happens.

To be noted the modern approach with fiber based direct links between two routers is to use the interface command

ip ospf network point-to-point

to avoid DR/BDR election and generation of Network LSA

So type 1 point to point applies to serial interfaces and those interfaces with a modified OSPF network type to point to point.

Hope to help

Giuseppe

[rookie R]

Thanks for the reply, it helps me a lot.

Would you mind answering another question for me? Does the word 'network' in the 'Transit network' meaning 'network segment'? Because every MA\NBMA network segment need to select DR\BDR 

[Giuseppe Larosa]

Hello @rookie R ,

>> Does the word 'network' in the 'Transit network' meaning 'network segment'?

Yes I agree

>> Because every MA\NBMA network segment need to select DR\BDR 

for NBMA it depends on the OSPF network type in use point to multipoint and point to multipoint non-broadcast do not elect DR/BDR if I correctly remember as they see the network segment as a collection of point to point links.

Hope to help

Giuseppe

[rookie R]

Appreciate your help, this transit\stub network bothered me for a while. Sometimes I think they make network protocol so complicated so that we can all fail about the test. There are so many 'stub' in OSPF, for example, there are stub area, stub host, stub network, I know they want to save memory, but the names are so confusing