[c-nsp] Routing performance of ME3400

Garry gkg at gmx.de
Wed Oct 27 10:17:33 EDT 2010


Hi,

I'm trying to pinpoint a problem with a customer site ... it's hooked up
via dual 1G SM to a central 4500. There are multiple VLANs connected.

Weird thing is this:

VLAN 999 is distributed on L2 between three sites - the customer, the
site with the 4500, and the backbone site. All three boxes have L3
addresses in that VLAN.
VLAN 1999 is used only at the customer site, with its own IP subnet.

The backbone site has additional VLANs, one of which has a Linux server.

When I hook up a PC to the customer site switch, using VLAN 999 and
another IP out of the VLAN, doing an iperf run results in "appropriate"
throughput in either direction (server only has 100M, so the 95-98mbit
iperf reports should be OK). In this setup, the ME3400 only does L2 with
the packets.

Doing the same using VLAN 1999, with an IP out of that IP range, and the
ME3400 doing L3 forwarding, incoming (towards the customer site) traffic
throughput drops to something like 30-50Mbit, while outgoing throughput
results in a constant (!) 16777 kbit. Remember, this is still on a 2GB
PortChannel in uplink!

Even worse, on bidirectional traffic (incoming 30mbit e.g.), output even
drops further, as if there were some Halfduplex issue (which there
isn't, at least not on any interface involved, checked everything
multiple times).

Could it be that the ME3400, albeit having the "largest" IOS on it
(metro-ipacess) for BGP etc., is severely limited as far as L3
performance goes? Also, I'm sporadically seeing this error:

*Mar  1 00:41:15.366: %PLATFORM_UCAST-4-PREFIX:  One or more, more
specific prefixes could not be programmed into TCAM and are being
covered by a less specific prefix, and the packets may be software forwarded

I did a "show platform ip unicast failed route" and got this output:

Entries covered by Actual default route(0.0.0.0/0)
                  240.0.0.0/4 Tbl:0 : Cover:0.0.0.0/0 Tbl:0
                  0.0.0.0/8 Tbl:0 : Cover:0.0.0.0/0 Tbl:0
                  127.0.0.0/8 Tbl:0 : Cover:0.0.0.0/0 Tbl:0
                  x.x.y.0/24 Tbl:0 : Cover:0.0.0.0/0 Tbl:0
                  x.x.x.y/29 Tbl:0 : Cover:0.0.0.0/0 Tbl:0
        Total of 5 entries covered by 0.0.0.0/0 Tbl:0
Entries covered by Actual default route(0.0.0.0/0)
                  240.0.0.0/4 Tbl:1 : Cover:0.0.0.0/0 Tbl:1
                  0.0.0.0/8 Tbl:1 : Cover:0.0.0.0/0 Tbl:1
                  127.0.0.0/8 Tbl:1 : Cover:0.0.0.0/0 Tbl:1
        Total of 3 entries covered by 0.0.0.0/0 Tbl:1
Entries covered by Actual default route(0.0.0.0/0)
                  240.0.0.0/4 Tbl:2 : Cover:0.0.0.0/0 Tbl:2
                  0.0.0.0/8 Tbl:2 : Cover:0.0.0.0/0 Tbl:2
                  127.0.0.0/8 Tbl:2 : Cover:0.0.0.0/0 Tbl:2
                  10.10.0.0/16 Tbl:2 : Cover:0.0.0.0/0 Tbl:2
        Total of 4 entries covered by 0.0.0.0/0 Tbl:2

Checking Cisco's docs, the "recommended action" isn't really useful:

Quote: "Recommended Action    No action is required. "

Great. So seeing that CPU might be used for L3 forwarding does not
warrant any action? Seeing that 0/8 route there has me somewhat worried,
but what might cause the performance hit is the other two network routes
listed as being covered by 0/0 ... any comments on this? Can I avoid it
somehow? Anyway, the customer site at the moment does not report this
error, but performance is still bad, so I reckon it's not necessarily
caused by this ...

Hints appreciated!

Tnx, Garry


More information about the cisco-nsp mailing list