Vpls split horizon

Created: Feb 24, 2020 04:48:14Latest reply: Feb 27, 2020 21:28:21 125 7 0 0
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Looking at vpls loop avoidance guidelines, it's stated that each PE need to support split horizon. But i didn't found a way to check if it's enabled on PW. Is it active by default on s67xx séries ?


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chenhui
Admin Created Feb 24, 2020 07:07:01 Helpful(2) Helpful(2)

Hi @AGregory,
Yes, split horizon is enabled by default.
You can disable the split horizon using command pw spoke-mode, what should be pointed out is that the split horizon could be disabled when adopting the BGP-AD VSI.
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sohaib.ansar
sohaib.ansar MVE Created Feb 24, 2020 05:03:04 Helpful(0) Helpful(0)

Hi User,
The design of many routing protocols considers the routing loop problem. The routing protocol itself has the anti-loop feature. For example: the SPF algorithm of OSPF and IS-IS, BGP as-path feature, the originator-id and cluster-id of BGP Route Reflector, and protocol summarization route are always accompanied by routes pointing to the NULL0 interface. However, the multi-protocol combination networking breaks the natural loop protection feature of a single protocol. Therefore, the routing loop problem is easy to occur. Therefore, we must face the problem of routing loops when multiple protocols are interoperable during network design or cutover. How to design an effective method to avoid this problem is difficult. This post lists several methods to avoid loops caused by multiple protocol interoperations. I hope this will help you in your future work.



1. Use the Route TAG flag and adjust the protocol priority.

l A tag is added during the distribution to mark that the route has been distributed. In reverse distribution, the original protocol is not released.

l When a route with a lower protocol priority is redistributed to a protocol with a higher protocol priority, increase the priority of the route.

l This method applies to scenarios where a large number of routes need to be distributed and the prefixes are irregular.

2. Use the prefix-list, access control list, and other tools to match routes and adjust the protocol priority.

l The routes that are originated by their respective protocols are matched during distribution. Only these routes can be redistributed, and other routes are rejected.

l When a route with a lower protocol priority is redistributed to a protocol with a higher protocol priority, increase the priority of the route.

l This method applies to scenarios where small routes need to be distributed and the prefixes are regular.



Example: The following figure shows the topology of a project. OSPF is enabled for Legacy Network, IS-IS is enabled for New Network, OSPF neighbor relationship established between New TR and TR/RR, OSPF neighbor relationship established between New POP/RR and BNG, and OSPF/IS-IS neighbor relationships established between the two IGWs.

showimage-14121283-171905-c5f510d81430c3

Point A:

1. OSPF:

l If the priority of the route with TAG 124792 remains unchanged, the route is still 150. Set the priority of other OSPF routes to 10, because the IS-IS priority is 15. Otherwise, the routes advertised by the OSPF source will preferentially select the IS-IS route, and a loop occurs. This is an example of adjusting the priority of the route with a lower protocol priority so that the source route is preferentially selected.

l Change the priority of the IGW route to 150. Otherwise, the New TR selects Old TR when selecting an IGW.

The loop protection measures are often accompanied by the adjustment of the protocol priority. The two are mutually reinforcing.

2. When importing OSPF routes to IS-IS:

l The route with TAG 124792 is rejected because it is imported from IS-IS to OSPF on New TR and should not be re-imported to IS-IS.

l The route with TAG 6032 is rejected because it is imported from IS-IS to OSPF on New POP and should not be re-imported to IS-IS.

l Allow other OSPF routes because the routes are advertised by the OSPF source and add TAG 124791.

3. When importing IS-IS routes to OSPF:

l The route with TAG 124791 is rejected because it is imported from OSPF to IS-IS on New TR and should not be imported to OSPF again.

l Allow routes with TAG 603 and add TAG 124792.

l Reject other IS-IS routes.





Point B:

1. IS-IS:

l The priority of the IS-IS route with TAG 603 is downgraded to 180.

2. When importing OSPF routes to IS-IS:

l The route with TAG 124792 is rejected because it is imported from IS-IS to OSPF on New TR and should not be re-imported to IS-IS.

l The route with TAG 6032 is rejected because it is imported from IS-IS to OSPF on New POP and should not be re-imported to IS-IS.

l Allow other OSPF routes because the routes are advertised by the OSPF source and add TAG 603.

3. When importing IS-IS routes to OSPF:

l The route with TAG 603 is rejected because it is imported from OSPF to IS-IS on New POP and should not be imported to OSPF again.

l Allow some IS-IS routes to OSPF and add TAG 6032.

l Reject all other IS-IS routes.



Point C:

1. IS-IS:

l Adjust the priority of the IS-IS route with TAG 124791 to 180 so that the route is lower than the OSPF route. Optimize IGW route selection so that the route to the OSPF source is still OSPF.



It can be seen that multi-point bidirectional redistribution routing loops between different IGPs are complex. Avoid using multiple routing protocols during network design and cutover to avoid interaction between them and reduce complexity and risks.
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sohaib.ansar
sohaib.ansar MVE Created Feb 24, 2020 05:08:48 Helpful(0) Helpful(0)

hi @AGregory
yes you can configure it through VPLS.
for more information you can visit below link.
https://support.huawei.com/enterprise/en/doc/EDOC1000178179/e3c35319/loop-prevention
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chenhui
chenhui Admin Created Feb 24, 2020 07:07:01 Helpful(2) Helpful(2)

Hi @AGregory,
Yes, split horizon is enabled by default.
You can disable the split horizon using command pw spoke-mode, what should be pointed out is that the split horizon could be disabled when adopting the BGP-AD VSI.
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AGregory
AGregory MVE Created Feb 24, 2020 13:02:07 Helpful(0) Helpful(0)

Thanks all. We're using kompella vpls, so as stated by @chenhui, it's enabled by default.
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lucian2003
lucian2003 MVE Created Feb 24, 2020 22:16:52 Helpful(0) Helpful(0)

Great
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Hello%20friends%2C%20I%20am%20a%20Telecommunications%20and%20electronics%20engineer%20and%20I%20just%20graduated%20as%20a%20master%20in%20telecommunications%20systems.%20I%20work%20in%20the%20telecommunications%20company%20of%20Cuba%2C%20ETECSA.%20I%20am%2035%20years%20old%20and%20I%20attend%20the%20transport%20network%20in%20my%20province%2C%20which%20is%20mainly%20Huawei.
chenhui
chenhui Admin Created Feb 25, 2020 00:36:10 Helpful(0) Helpful(0)

Posted by AGregory at 2020-02-24 13:02 Thanks all. We're using kompella vpls, so as stated by @chenhui, it's enabled by default.
You are welcome. :D
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welisson_br
welisson_br Created Feb 27, 2020 21:28:21 Helpful(0) Helpful(0)

What about martini? Is it possible to disable as well?

Cheers
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