cbwfq on multilink laboratory setup

[b0y37]

Hi there.

I have a multilink laboratory setup, composed of two Cisco routers back to back. One is an Cisco ISR 1841 and the other is a Cisco3745.I configured both of them for multilink and setup a cbwfq for qos. But it appears that (my monitoring tool is PRTG, btw) the routers does not dedicate my specified bandwidth between two hosts.

For reference, "sh ver" output from the 1841:

Cisco IOS Software, 1841 Software (C1841-IPBASE-M), Version 12.3(8)T11, RELEASE
SOFTWARE (fc1)
Technical Support:

http://www.cisco.com/techsupport

Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Wed 10-Aug-05 15:43 by dchih

ROM: System Bootstrap, Version 12.3(8r)T9, RELEASE SOFTWARE (fc1)

And here is my running config:Current configuration : 1617 bytes
!
version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname ISR1841
!
boot-start-marker
boot-end-marker
!
no logging console
!
mmi polling-interval 60
no mmi auto-configure
no mmi pvc
mmi snmp-timeout 180
no aaa new-model
ip subnet-zero
ip cef
!no ip domain lookup
no ftp-server write-enable
!
!
!
class-map match-any MIX
description prioritize critical traffic
match access-group 102
!
!
policy-map prioritize_mimix
class MIX
priority 5000
class class-default
fair-queue
!
!
!
interface Multilink1
ip address 10.1.0.154 255.255.255.252
service-policy output prioritize_mimix
ppp multilink
ppp multilink fragment delay 1
ppp multilink interleave
ppp multilink group 1
ppp multilink multiclass
!
interface FastEthernet0/0
ip address 10.89.0.254 255.255.0.0
duplex auto
speed auto
!
interface FastEthernet0/1
no ip address
duplex auto
speed auto
!
interface Serial0/1/0
bandwidth 4000
ip address 192.168.1.2 255.255.255.0
encapsulation ppp
no fair-queue
ppp multilink
ppp multilink group 1
!
interface Serial0/1/1
bandwidth 4000
ip address 192.168.2.2 255.255.255.0
encapsulation ppp
no fair-queue
ppp multilink
ppp multilink group 1
!
interface Async0/0/0
no ip address
!
interface Async0/0/1
no ip address
!
ip classless
ip route 10.88.0.0 255.255.0.0 10.1.0.153
ip route 10.90.0.0 255.255.0.0 10.1.0.153
ip http server
!
!
access-list 102 permit ip any host 10.88.0.1
ip classless
ip route 10.88.0.0 255.255.0.0 10.1.0.153
ip route 10.90.0.0 255.255.0.0 10.1.0.153
ip http server
!
!
access-list 102 permit ip any host 10.88.0.1
!I even tried access-list 102 permit ip host 10.89.0.1 host 10.88.0.1
!
control-plane
!
!
line con 0
line aux 0
line 0/0/0 0/0/1
stopbits 1
speed 115200
flowcontrol hardware
line vty 0 4
login
!
end

"sh ver" for the C3745:
IOS (tm) 3700 Software (C3745-I-M), Version 12.2(13)T1, RELEASE SOFTWARE (fc1)
TAC Support:

http://www.cisco.com/tac

Copyright (c) 1986-2003 by cisco Systems, Inc.
Compiled Fri 03-Jan-03 15:12 by ccai
Image text-base: 0x60008940, data-base: 0x60C28000

ROM: System Bootstrap, Version 12.2(8r)T2, RELEASE SOFTWARE (fc1)

Running config for the cisco3745:
version 12.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname C3745
!
no logging console
no logging monitor
!
ip subnet-zero
!
!
no ip domain lookup
!
class-map match-any MIX
description prioritize critical traffic
match access-group name mimix_priority

!policy-map mimix
class MIX
priority 5000
class class-default
bandwidth 1000
!
!
!
!
!
interface Multilink1
ip address 10.1.0.153 255.255.255.252
max-reserved-bandwidth 90
service-policy output mimix
ppp multilink
ppp multilink fragment-delay 1
ppp multilink interleave
multilink-group 1
!
interface FastEthernet0/0
ip address 10.88.0.254 255.255.0.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 10.90.0.254 255.255.0.0
duplex auto
speed auto
!
interface FastEthernet4/0
no ip address
shutdown
duplex auto
speed auto
!
interface Serial4/0
bandwidth 4000
no ip address
encapsulation ppp
clockrate 4000000
no fair-queue
ppp multilink
multilink-group 1
!
interface FastEthernet4/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial4/1
bandwidth 4000
no ip address
encapsulation ppp
clockrate 4000000
no fair-queue
ppp multilink
multilink-group 1
!
ip flow-export version 5
ip flow-export destination 10.89.0.1 17
ip classless
ip route 10.89.0.0 255.255.0.0 10.1.0.154
ip http server
!
!
ip access-list extended mimix_priority
permit ip host 10.88.0.1 host 10.89.0.1

!
snmp-server community ****** RO
snmp-server enable traps tty
snmp-server host 10.88.0.1 ******
!
line con 0
line aux 0
line vty 0 4
login
!
end


I tested my setup using various ftp sessions between
10.89.0.1 (server) to 10.88.0.1 and 10.90.0.1. But i noticed that the bandwidth are just divided equally among the ftp sessions(fair-queue?). My goal is to have a constant 5Mbps between 10.89.0.1 and 10.88.0.1.

I have been playing with commands like ppp multilink multiclass and the fair-queue command, but i cant seem to make it work.

Any more ideas?
TIA

 

[b0y37]

or maybe am I not generating enough traffic/congestion to trigger CBWFQ?

 

[brianinms]

The most you can get out of those 2 serial interfaces in a multilink group is 3mb.

 

[b0y37]

3Mb? Why?
When I measured the bandwidth using PRTG, I got 8Mb. I monitored 3 Ports of the 3745 - multilink1, fa0/0 and fa0/1. I got a constant 8Mb on multilink1 and varying BW on fa ports depending on the number of ftp sessions. I have one ftp session between 10.88.0.1 and 10.89.0.1. And 4 ftp sessions between 10.90.0.1 and 10.89.0.1. I noticed that Fa0/1 has a higher bandwidth, which is equal to (ftp sessions on fa0/1)/(ftp sessions on fa0/0 and fa0/1). This looks like fair-queue, doesnt it?

 

[brianinms]

A normal T1 connection, hence serial interface is 1.5mb. You combine 2 of them and you get 3mb. Post a show ver from each router.

 

[b0y37]

IC. But its just a lab setup. I used a DCE/DTE cable to connect the two routers. I configured the BW of each of the serial int to be 4Mb. Sorry for missing out this info.

show ver:
Cisco IOS Software, 1841 Software (C1841-IPBASE-M), Version 12.3(8)T11, RELEASE
SOFTWARE (fc1)
Technical Support:

http://www.cisco.com/techsupport

Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Wed 10-Aug-05 15:43 by dchih

ROM: System Bootstrap, Version 12.3(8r)T9, RELEASE SOFTWARE (fc1)

ISR1841 uptime is 30 minutes
System returned to ROM by power-on
System image file is "flash:c1841-ipbase-mz.123-8.T11.bin"

cisco 1841 (revision 6.0) with 118784K/12288K bytes of memory.
Processor board ID FHK1020520H
2 FastEthernet interfaces
2 Serial interfaces
2 Serial(sync/async) interfaces
2 terminal lines
DRAM configuration is 64 bits wide with parity disabled.
191K bytes of NVRAM.
31360K bytes of ATA CompactFlash (Read/Write)

Configuration register is 0x2102

 

[brianinms]

A serial interfaces bandwidth is 1.5mb. Using the bandwidth statement merely changes the bandwidth as it is interpreted by routing protocols. Additionally the value after the bandwidth command is listed in kilobits.

 

[b0y37]

Ok, I think I understand. But why does my download time halved when I increased the BW from 2Mbps to 4Mbps?
Also, why is the serial link limited to T1 speed, when I can get a leased line of higher bandwidth, say E1?

show int s0/1/0:

Serial0/1/0 is up, line protocol is up
Hardware is GT96K Serial
Internet address is 192.168.1.2/24
MTU 1500 bytes, BW 4000 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, LCP Open, multilink Open

 

[b0y37]

So is my running-config ok?

 

[Minue]

Hello
The maximum speed for the a serial interface is E1 speed 2044.So you should set your clock rate to 2000000.As brianinms said,the bandwidth command is use for routing protocols to calculate its'"metric" correctly.It strange that changing bandwith gives you different results.
To make things less complicated leave out the multilink,just use the standard link.Wen you get things working then you can try the multilink.
As far as the QoS is concerned remember that it only kicks in when the link is congested enough.Maybe you aren't generating enough traffic.So this is another reason that you should use lower link speeds.
Also try posting a "show policy-map interface"So we can see if the traffic is being classify.
Regards

 

[b0y37]

Thanks for the reply, Minue.
I will test the setup again using standard link, with lower link speed.

Sorry, for the ignorance, still a newbie in the networking world. =)

So, however high I set the bandwidth and clockrate for the interface, the maximum speed will still be at T1 or E1? Im a little confused with what brianinms and you said about the maximum link speed for a serial interface.

 

[Minue]

Hello
You are welcome!I know it's hard to understand some networking topics.Even with good books sometime the concept aren't explain well.
Network layer 1 technologies have physical data rate limits.The 56K modem is an example,so the T1/E1 has it limits too.Does higher clock rate on the IOS,would be for other technologies.
Feel free to ask any question you want,so asto help you understand.
Regards

 

[b0y37]

To answer my own question, i think it depends on the hardware. Ive read that a WIC-2T on a 3745 supports 8Mbps, and a HWIC-4A/S on a 1841 only supports 256kbps. I knew that the "bandwidth" command on an interface does not change the maximum speed the interface supports. I just didnt realize that the maximum speed can be as low as 256kbps on a particular interface. Ill check out the routers' technical module tomorrow when i get to work.

 

[Minue]

Hello
You are right!I just google it.I guess there's alway something learn.

http://www.cisco.com/en/US/products/hw/routers/ps274/products_tech_note09186a00800b0858.shtml

Anyway this isn't a rule of thumb.The physical technologies limits normally is the regular .It's just that cisco breaks the reals sometimes to push their market.If you read the document well,you will see some limitations.First you will need a special module.Then there's a speed backplane problem.Also I haven't seen a WIC-2T deployed with 8MB.Tommorow I check this out at work or maybe ask my work-mates that deals with the Layer 1 provisioning.
Regards