Cisco 4500x VSS MEC

[Network Pro]

Hi,

Does Cisco 4500x VSS MEC support LaCP with Cisco 2960s series switches ? or what is the other solution - is it better to use fast hello packet ?

Thanks

[Reza Sharifi]

Hi,

If you are planning to uplink 2960s to a set of 4500 (VSS) using LACP, that is support it, but this is not a solution to replace fast hello.  Fast hello can be replaced by ePAGP.  Most versions of IOS-XSs support ePAGP for dual active detection and some newer versions now support fast hello.

HTH

[Network Pro]

which is the better method ? epagp or fast hello ? i am using cisco 2960s stackable switches and will need to use lacp in some instantaces

[Reza Sharifi]

If your IOS support it use fast hello.

HTH

[Network Pro]

Thanks how to avoid spilit brain scenario when we lose vsl links ? can i use role priority ?

[Reza Sharifi]

As long as you have two VSL links from 2 different modules, you should be fine. Priority role is not going to make a difference.

[Network Pro]

Reza i have a question,

if i dont have priority and if  the active switch fails  or vsl link fails then how is the access switch going to know which is master (wont it be spilit brain ?)

2. will 2960s stackable switches work with lacp and pagp with cisco 4500x in vss mode (i.e for lacp - active / active and pagp - desirable / desirable) because i read somewhere that pagp cant be used

please note - i am using a old version of ios on cisco 4500x that does not support fast hello - i need to use only dual-active detection pagp)

[nspasov]

PAgP is not supported on a cross-stack etherchannel, only LACP. So if you want to use ePAgP then you either have to build a port-channel to a single switch. If it is a stack then the port-channel must terminate on a single stack member. If neither one of those are an option then you can use fast-hello where you would dedicate a port on each chassis and establish a direct connection. One caveat for that is that you will need to run XE 3.5.x

Hope this helps!

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[Network Pro]

Thanks Neno, any thoughts on

if i dont have priority and if the active switch fails or vsl link fails then how is the access switch going to know which is master (wont it be spilit brain ?)

[nspasov]

The switch priority won't apply in your situation. Here is an extract from Cisco's VSS guide about priority:

Virtual Switch Priority

The selection of the switch member that is to become the active or hot-standby switch depends on the order and the way in which the switches are initialized. If the switch members boot simultaneously, the switch with the lowest switch ID becomes the active virtual switch. If each switch member boots at different times, then the switch that is initiated first becomes the active virtual switch regardless of switch ID. The VSS can also be configured with switch priority. Usually, the default switch priority (100) need not change.

Check out the link below which should answer most if not all of your questions about VSS and dual-active detection:

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/VSS30dg/campusVSS_DG.pdf

Thank you for rating helpful posts!