interface bandwith GRE on switch C3750G

[csco11579831]

Hello,

Can you please tell me how I can know the actual bandwidth on this interface?

I am doing research on the internet and I found, but it does not appear on my switch BBO this information:

Tunnel transmitted bandwidth 8000 (kbps)

Tunnel receive bandwidth 8000 (kbps)

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######### Here show a tunnel interface from my switch BBO  ##########

##############################################################

Switch#sh interfaces tunnel 1

Tunnel1 is up, line protocol is up

  Hardware is Tunnel

  Description: Vers_BBO_1

  Internet address is 192.168.1.46/30

  MTU 1514 bytes, BW 100 Kbit, DLY 50000 usec,

     reliability 255/255, txload 54/255, rxload 1/255

  Encapsulation TUNNEL, loopback not set

  Keepalive not set

  Tunnel source x.x.x.x destination x.x.x.x

  Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled

  Tunnel TTL 255

  Checksumming of packets disabled, fast tunneling enabled

  Last input 3w2d, output 00:00:00, output hang never

  Last clearing of "show interface" counters never

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/0 (size/max)

  5 minute input rate 0 bits/sec, 0 packets/sec

  5 minute output rate 444000 bits/sec, 185 packets/sec

     47 packets input, 5458 bytes, 0 no buffer

     Received 0 broadcasts (0 IP multicasts)

     0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

     120238749 packets output, 36159257307 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 output buffer failures, 0 output buffers swapped out

[Vasilii Mikhailovskii]

Hello.

Actuial bandwidth of the tunnel is dependent on the bandwidth of transiting physical interface.

If rout to the peer (destination) goes via Gig ports, then bandwidth should be same as Gig minus 5-7% (overhead for GRE encapsulation).

PS: at the same time if the tunnel goes over WAN you should take into account the bottrlenecks bandwidth.

PS2: I'm not sure if 3750 switch can be an end-point for GRE tunnel.

[csco11579831]

Hello MikhailovskyVV,

Thank you for your answers,

3570 switch can be an end point for the GRE tunnel, and I work with him,

So if only 45MB of bandwidth, the speed will not exceed 3 MB

Is it possible to increase the bandwidth and how?

Is it possible to have explanations regarding the two line below:

Tunnel Transmitted bandwidth 8000 (kbps)

Tunnel receive bandwidth 8000 (kbps)

and why it is not present in my configuration?

[Peter Paluch]

Hi,

A Tunnel interface is nothing more than just a process of putting another layer of headers onto an existing datagram to protect or hide its internal headers. There is no physical interface related to the operation of a Tunnel interface. Once a tunneled packet is created, it is forwarded through some other physical interface on the device that performs the tunneling.

There are two possible bottlenecks that ultimately define the bandwidth as seen by a Tunnel interface. The first bottleneck is the CPU of the router if the tunneling operations are performed in the operating system and not in specialized hardware. Too many packets to be tunneled can easily overwhelm the CPU and its capabilities. The second bottleneck is the physical inteface itself that will be used to send out the tunneled packet.

On Catalyst 3xxx switches, there is no hardware support for tunneling operations, meaning the GRE tunneling encapsulation and decapsulation is performed in software and must be executed on the CPU. While there is no official benchmark as far as I know, I estimate that with the CPU in a Cat3750G, the throughput of a GRE tunnel is, at most, in orders of Mbps or tens of Mbps in ideal conditions. I do not think anyone will be willing to guarantee this figure, as these devices are not really intended to terminate GRE tunnels.

Apart from that, however, you do not really care about the bandwidth command setting on Tunnel interfaces, as that command has no influence on the real throughput of this interface - it just influences routing protocols like OSPF and EIGRP in their best path selection, and it may impact QoS mechanisms if applied to the Tunnel interface. However, if none of this is of a concern, simply configure the bandwidth command on a Tunnel interface to, say, 1000 (meaning 1Mbps) and you should be fine.

Best regards,
Peter