OSPF on the ISR 1000 series.

[Vyacheslav_Emchuk]

I ask owners of ISR 1000 series devices to tell me what is the average time to restore the OSPF channel after rebuilding when using these devices.

[balaji.bandi]

Not sure we able to understand your question, OSPF neighbour will be formed based on partner available.

as soon as device see partner it form the neighbourship ?

is this what you looking, if not please explain more ?

[Georg Pauwen]

Hello,

your ISR 1000 supports incremental SPF, which makes for faster convergence. Here is an excerpt from the document linked below:

Information About OSPF Incremental SPF
OSPF uses Dijkstra’s SPF algorithm to compute the shortest path tree (SPT). During the computation of the SPT, the shortest path to each node is discovered. The topology tree is used to populate the routing table with routes to IP networks. When changes to a Type-1 or Type-2 link-state advertisement (LSA) occur in an area, the entire SPT is recomputed. In many cases, the entire SPT need not be recomputed because most of the tree remains unchanged. Incremental SPF allows the system to recompute only the affected part of the tree. Recomputing only a portion of the tree rather than the entire tree results in faster OSPF convergence and saves CPU resources. Note that if the change to a Type-1 or Type-2 LSA occurs in the calculating router itself, then the full SPT is performed.

Incremental SPF is scheduled in the same way as the full SPF. Routers enabled with incremental SPF and routers not enabled with incremental SPF can function in the same internetwork.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-16-6/iro-xe-16-6-book/iro-incre-spf.html

[Joseph W. Doherty]

Do you mean after a link comes (back?) up, how long does it take for the ISR to form an OSPF adjacency and start routing using whatever information was obtained from the "new" neighbor?

I recall time is usually in seconds.  However, I also recall time varies based on different variables.

For example, speed of the connecting link will dictate how fast the neighbor's LSAs can be delivered.

Size and complexity of the local OSPF area topology (i.e. SPF calculation time) and how many non-area routes.

Whether incremental SPF is active or not.  If incremental SPF is active, how the new neighbor's information benefits, or not, from incremental SPF.

I would expect "faster" CPUs to perform their OSPF calculations faster, but I recall even the earlier 800 series weren't slow enough that OSPF adjacency and route computation time were a concern.  Do you have a reason to be concerned?

[Vyacheslav_Emchuk]

Hello Joseph!

Yes, that's what I meant. I am interested in how much time in seconds it will take to start routing.

I have OSPF running on my test stand between two routers from another manufacturer. The scheme is simple. They are connected directly. It takes approximately 10 seconds to start routing. It's a long time...

How many seconds do you think it will take two ISR 1000 series routers to start routing under the same conditions?

Thanks)

[Georg Pauwen · Accepted solution]

Hello,

ten seconds seems excessive. What brand/model are these routers ? On Cisco routers (including your ISR 1000), it usually takes a few seconds at most for the OSPF neighborships to form, and for the routers to start routing.

[Vyacheslav_Emchuk]

Thanks for the answer!

I have Zyxel USG 60 routers on my test stand. to run on the OSPF network, I will use Cisco routers, they were faster )

[Georg Pauwen]

Hello,

the problem might be the OSPF poll interval setting on your Zyxel routers. Check the OSPF Configuration page (Step 14 in the document linked below), and set that value to the lowest value possible on all participating routers.

https://kb.zyxel.com/KB/searchArticle!gwsViewDetail.action?articleOid=007151&lang=EN