Functionality of "tunnel bandwidth" statement.

Unanswered Question

Does the "tunnel bandwidth" statement (not the regular "bandwidth" statement as applied to a tunnel) apply to mGRE tunnels?

The only Cisco documentation I've seen regarding this statement has been in the context of RBSCP (Rate Based Satellite Control Protocol), not mGRE.

The reason I ask this is that in the case of an mGRE tunnel defined roughly as follows:

interface Tunnel1

bandwidth 15000

ip address

tunnel source FastEthernet0/0

tunnel mode gre multipoint




...the output of "show interface Tunnel1" shows:

Tunnel transmit bandwidth 8000 (kbps)

Tunnel receive bandwidth 8000 (kbps)

...8000 kbps being the default setting for "tunnel bandwidth". (8000 kbps is shown regardless of the actual bandwidth, so long as the "tunnel bandwidth" statement is not used.) Adding the "tunnel bandwidth transmit 15000" and "tunnel bandwidth receive 15000" statements will change the output of "show interface", but do they have any actual operational effect? The regular "bandwidth" statement seems to be used in EIGRP and bandwidth utilization calculations (such as rxload and txload, seen in the same "show interface" output).

In addition, the documentation indicates that "tunnel bandwidth receive" statement has been deprecated, so this discussion really only pertains to "tunnel bandwidth transmit".

I believe I am getting more than 8000 kpbs per second, but for logistical reasons I can't test this properly in a production environment.

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Tunnel Bandwidth statement is also applied to mGRE tunnels. The "tunnel mode" command is used to specify the tunnel mode in mGRE.After enabling mGRE tunneling, you can enable the tunnel protection command, which allows you to associate the mGRE tunnel with an IPSec profile. Combining mGRE tunnels and IPSec encryption allows a single mGRE interface to support multiple IPSec tunnels, thereby simplifying the size and complexity of the configuration.

That's interesting, because I actually got around to performing some tests in a non-production environment. I set up an IPSEC-over-mGRE tunnel over a 1.5 Mbps link and set the regular "bandwidth" statement accordingly. I verified the actual throughput by passing large quantities of data across the link using test utilities which gave me roughly the expected figures. I then added "tunnel bandwidth receive 200" and "tunnel bandwidth transmit 200" statements to the tunnel interfaces, saved the configs, and restarted both routers. I repeated the throughput tests and got approximately the same results. If these statements had any effect I would expect to see a limitation in throughput to somewhere in the neighborhood of 200kbps. Perhaps someone else can actually try this. So far I have seen no effect other than changing what is shown in the "show interface" output.

(Note, also that the example in the documentation you linked to specifically refers to an RBSCP tunnel.)


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