Category: General Networking

We had a recent scenario where two different customers in the same building shared the same Cisco 3550. Now I can hear you saying – but 3550’s are defunct! – well yes they are, but at the same time there are plenty out there still…

So anyway the two customers had two different bandwidth requirements, and they shared the same upstream link. Customer A needed to be capped at 15mbps and customer B needed to be capped at 25mbps. Well I thought, should be fairly straightforward – I’ll configure a policy map and I’ll be done in half and hour.

Yeah well, that was the idea. It didn’t work so as a last resort I hit Cisco’s web site and found this document:

http://www.cisco.com/en/US/products/hw/switches/ps646/products_tech_note09186a00800feff5.shtml

Bingo! (I thought) I’ll just follow this and it’ll all work fine and dandy. Did it work? Did it bananas!

At this point my head was starting to fizz! Scouring Google revealed various no luck losers like myself trying to get the solution to work. Eventually I stumbled on some CCIE notes that stated something to the effect of “the DSCP bit has to change internally on the switch for QoS to work” – hmm, what the heck I’ll give it a go, and if Bob’s not your uncle, it worked – phew!

One caveat thought – this is inbound rate-limiting. If I can get outbound working (on the same device) without my head exploading I’ll let you know.

Here’s the config:

mls qos
!
class-map match-all ip-in
match access-group 100
class-map match-all ip-out
match ip dscp 1
!
policy-map capped-15mbps
class ip-out
police 15000000 2000000 exceed-action drop
policy-map capped-25mbps
class ip-out
police 25000000 2000000 exceed-action drop
policy-map ip-in
class ip-in
set ip dscp 1
!
interface FastEthernet0/1
description upstream WAN port
no switchport
ip address x.x.x.x 255.255.255.252
no ip redirects
no ip proxy-arp
no ip mroute-cache
load-interval 30
service-policy input ip-in
hold-queue 200 in
hold-queue 200 out
!
interface FastEthernet0/2
description Local port connected to customer A (capped at 15mbps)
no switchport
ip address x.x.x.x 255.255.255.248
no ip redirects
no ip proxy-arp
no ip mroute-cache
load-interval 30
service-policy output capped-15mbps
!
interface FastEthernet0/3
description Local port connected to customer B (capped at 25mbps)
no switchport
ip address x.x.x.x 255.255.255.248
no ip redirects
no ip proxy-arp
no ip mroute-cache
load-interval 30
service-policy output capped-25mbps
!
access-list 100 permit ip any any