Counterplan for unidirectional link failure of WAN (dedicated line)

[omatsu]

If anyone has experience in dealing with unidirectional link failures in WAN lines (dedicated lines), please give me some advice.

Our two offices are connected by bundling two dedicated lines with a static LAG to provide redundant routes (The dedicated lines have a link pass-through function, so redundancy can be achieved with the LAG).

Currently, the switch interface that connects the leased line is in automatic mode, but due to changes in the leased line specifications, it will be necessary to change it to fixed mode.

Therefore, when fixing interfaces, we need to consider countermeasures against unidirectional link failures.
What is the best way to deal with unidirectional link failures in leased lines?

I'm currently thinking about using UDLD or LACP, but I'm wondering if there will be any problems using it over a WAN line.
In addition, the distance between the two offices is several hundred kilometers, and the latency time (RTT) is about 10 msec.

<postscript>
I have attached the current configuration diagram.

[balaji.bandi]

Leased Lines means - is this Ethernet delivery ? Fibre or Copper  end side ?)

UDLD is good if you have dark fibre connected between site.

If so many Providers involved - may not help as expected.

LACP you can use if they are delivered Layer 2 Links for high availability and bundling more links.

[omatsu]

Thank you for answering.

The leased line is Fiber.
At each site, the switch accommodating the leased line is connected to the line operator's equipment using 1000base-sx.
The specifications allow layer 2 protocols such as LACP and UDLD to flow on the leased line.

[balaji.bandi]

In that case you can use those requirement and do the testing.

[omatsu]

Thank you for your reply.

> If so many Providers involved - may not help as expected.
Our leased lines consist of only a single line operator's equipment.

In general, is it okay to use UDLD or LACP between switches that are several hundred kilometers apart (with a delay time RTT of 10ms)?
(Of course I think it is necessary to test .)

[balaji.bandi]

yes nexus do support UDLD and you can configure with LACP.

you can use below guide to test UDLD :

https://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/nx-os-software/118908-technote-udld-00.html

Create a Port-channel using below guide between nexus :

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/7-x/interfaces/configuration/guide/b_Cisco_Nexus_9000_Series_NX-OS_Interfaces_Configuration_Guide_7x/configuring_port_channels.pdf

you can then enable vPC on port-channel (since its good to have vPC between nexus device, if this is Layer 2 only)

[omatsu]

Sorry, my explanation and English may not have been good enough.
I knew that I could configure UDLD and LACP on Nexus.
I wanted to know if it is possible to configure UDLD or LACP even between switches separated by long distances (RTT delay time 10ms)

Thank you for your kindness in providing the URL of the document.

[MHM Cisco World]

LAG to lacp! 

Lacp use between two SW/R

LAG is use between more than two SW/R i.e. one side emulate to be virtual one.

I need more info about your topolgy 

MHM

[omatsu]

Thank you for your reply.

> I need more info about your topolgy 
I have added a configuration diagram to the first post, so please check it out.

In general, is it okay to use LACP between switches that are several hundred kilometers apart (with a delay time RTT of 10ms)?

[MHM Cisco World]

First it l2 connect ?

Second lacp is use when there are two or more link in bundle' if there is only one some SW put thr PO with one port into suspended.

Udld only use for optic fibers.

For long distance and you have optic fiber and one link then the best option is udld.

MHM

[omatsu]

Thank you very much for your reply.

> Do you want to connect l2 first?
Yes, it's L2 connect.

> For long distance and you have optic fiber and one link then the best option is udld.

I did a little testing today, and it seems that UDLD takes some time to put the interface into err-disabled state after detecting a unidirectional link failure, so I'd prefer LACP over UDLD if possible.
So, I would also like to consider adopting LACP by adding two dedicated lines so that Switch 1 and Switch 2 each have two port channel members .

In general, is it okay to use LACP between switches that are several hundred kilometers apart (with a delay time RTT of 10ms)?

[MHM Cisco World · Accepted solution]

Friend you can use both.

Two link (one port channel) use udld and lacp (mode fast).

The udld is more fast than lacp.

More more fast.

The udld detect unidirectional of fiber op one link ( the op fiber have two channels' one send and other receive' udld detect if one channel down)

Lacp add additional check to link (all fiber op link which meaning both channel)' and it protect from any l2 loop.

MHM

[omatsu]

I understand, thank you very much.
I would like to proceed with consideration based on your advice.