Remote-Span Vlan (what does this command do)?

[Aaron Street]

Hi, 

can any one tell me exactly what running the "remote-span" command under a vlan does? I know you use it for source and destination span sessions, but what changes to the vlan does this command actually achive? 

The reason I ask is that I want to trunk a Rspan vlan through a non RSPAN supporting switch but when i enable it on the trunk the remote switch (non RSPAN supporting)  shuts down the port as "inconsistent" and flags up the error with both the RSPAN vlan and the native vlan (running RPVST), it sees that running the command turns on SSTP on the RSPAN vlan but I wondered if there is any documentation showing more details on this. 

So to be clear I have three switchs, first is the source and supports rspan, second is non rspan and thrid also supports RSPAN and I want source to be on switch one, destination on switch 3 and switch 2 simple as a transient switch. 

Cheers 

[Julio E. Moisa]

Hi 

The remote span is to send traffic added to a vlan, first you must to create the remote span, it can be any vlan but with the following config:

Source Switch

vlan 100
remote-span

the remote vlan must be created on source an destination swtiches, then you can create the monitor session

conf t
monitor session 1 source interface g1/0/1 both   (example interface)
monitor session 1 destination remote vlan 100   

This vlan must be allowed under all the trunks on the path to the destination interface (if you are not applying restrictions on your trunk interface please omit this but be sure the remote vlan ID is passing to the destination), it the switch will receive the information, you should configure:

Destination switch.

monitor session 1 source remote vlan 100
monitor session 1 destination interface g2/0/1    (example interface)

Please check this link: http://www.networkstraining.com/how-to-configure-cisco-span-rspan-erspan/

Hope it is useful :-)

[Aaron Street]

Hi, 

sorry i think you missunder stand the question. I know how to use the rspan vlan (use it all the time), but what does the command "remote span" do? 

What is the technical differences between, 

vlan 10 and vlan 10 with Remote-span configured. 

how does a switch treat a vlan configures with remote span differently? it must make changes to how a vlan is treated or else there would be no need for the command. 

As mention I am trying to work out why a non cisco switch will not pass an RSPAN vlan when it it trunked to it and why it gets blocked by spanning tree. 

[Aaron Street]

I cant set the destination vlan on a monitor session to a vlan that is not configured as Remote span. so this command must to some thing other than simple indicate a vlan as a rspan vlan. 

[Julio E. Moisa]

Hi

The RSPAN VLAN carries SPAN traffic between RSPAN source and destination sessions. It has these special characteristics:

All traffic in the RSPAN VLAN is always flooded.
No MAC address learning occurs on the RSPAN VLAN.
RSPAN VLAN traffic only flows on trunk ports.
RSPAN VLANs must be configured in VLAN configuration mode by using the remote-span VLAN configuration mode command.
STP can run on RSPAN VLAN trunks but not on SPAN destination ports.
An RSPAN VLAN cannot be a private-VLAN primary or secondary VLAN.

For VLANs 1 to 1005 that are visible to VLAN Trunking Protocol (VTP), the VLAN ID and its associated RSPAN characteristic are propagated by VTP. If you assign an RSPAN VLAN ID in the extended VLAN range (1006 to 4094), you must manually configure all intermediate switches.

It is normal to have multiple RSPAN VLANs in a network at the same time with each RSPAN VLAN defining a network-wide RSPAN session. That is, multiple RSPAN source sessions anywhere in the network can contribute packets to the RSPAN session. It is also possible to have multiple RSPAN destination sessions throughout the network, monitoring the same RSPAN VLAN and presenting traffic to the user. The RSPAN VLAN ID separates the sessions.

This link could be useful: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swspan.html

[Aaron Street]

Cheers, 

but this seems to suggest rsan can run STP, 

but when i enable it and then try to trunk it to a Nexus switch I get this error, I know  the nexus does not support the "remote-span" command on a vlan but I am only trying to run this as a transient switch (in one trunk port and out another), if remove "remote-span" command on the vlan on the remote switch the issue goes away. So it seems that the command changes how the vlan operates in spanning tree.  

1) Event:E_DEBUG, length:107, at 129941 usecs after Mon Feb 6 14:14:09 2017
[105] stp_sstp_bad_pvid() port Po40 SSTP BPDU rcvd on VLAN 600, VLAN tag 1
making local port inconsistent

2) Event:E_DEBUG, length:105, at 129057 usecs after Mon Feb 6 14:14:09 2017
[105] stp_sstp_bad_pvid() port Po40 SSTP BPDU rcvd on VLAN 600, VLAN tag 1 making peer port inconsistent