Routing
Highlighted
Routing

OSPF Multi-area Routing

‎01-18-2020 04:48 AM

I have a question: 

 

If the R2-R4 link fails, which way will traffic route from R1 to R4? I am thinking it will follow the lwoest metric, but as it is across areas, is it correct to go R1 - R2- R3 -R4? 

 

Thanks 

 

Screenshot 2020-01-18 at 12.45.33.png

3 REPLIES 3
Highlighted
Routing

Betreff: OSPF Multi-area Routing

‎01-18-2020 08:06 AM

There is too less information in the exhibit to answer this for sure. However, if the links R1 - R2 - R3 - R4 are all inside area 0, then the packets will go this way, as the traffic will not leave area 0 to transit another area to go back to area 0 again.

--------------------------------------------------

If this solves your problem, please mark this post as "Accepted Solution".
If you think that my answer was helpful, please spend some Kudos.
Highlighted
Routing
Solution
Accepted by topic author NetworkMan23
‎01-19-2020 04:49 AM

Re: OSPF Multi-area Routing

‎01-18-2020 08:26 PM

Hello,

 


@NetworkMan23 wrote:

is it correct to go R1 - R2- R3 -R4? 

 


 

No. If this is pure IP forwarding (no MPLS and no tunnels of any sort: GRE, IPIP, IPSec etc) then when packet destined to R4 hits R2, then R2 has 2 choice routes:

- INTRA area 10 route from R4 via R5

- INTER area 0 route from R3

According to RFC 2328 section 11, INTRA area route is preferred and R2 will send this packet to R5 and R5 will forward to R4.

 

HTH

Thx

Alex

 

_____________________________________________________________________

Please ask Your Juniper account team about Juniper Professional Services offerings.
Juniper PS can design, test & build the network/part of the network as per Your requirements

+++++++++++++++++++++++++++++++++++++++++++++

Accept as Solution = cool !
Accept as Solution+Kudo = You are a Star !
Highlighted
Routing

Re: OSPF Multi-area Routing

‎01-18-2020 09:07 PM

Intra-area routes are preferred over inter-area routes regarless of the metric. If you wanted traffic going to R4 to be sent via R3 when the link R2<=>R4 fails, you can configure multi-area adjancency between R2 and R3 as shown:

multi-area adjacency.png 

protocols ospf {

area 0.0.0.0 {

   interface ge-0/0/0.0;

}

area 0.0.0.10 {

   interface ge-0/0/0.0 {

         secondary;

}

Yasmin Lara - Juniper Ambassador #QuadE - JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
JNCIS-CLOUD, JNCDS-DC, JNCIA-DevOps
Feedback