Introduction
This document describes on how to collect packet captures from the CLI of Connected Mobile Experience (CMX) 10.x server. These packet captures can aid in troubleshooting several scenarios (For example: NMSP communication between Wireless LAN Controller (WLC) and CMX server) to validate the communication flow.
Requirements
- Command Line Interface (CLI) access to the CMX server.
- Computer with Wireshark installed to read the captures in detail.
Using TCPDUMP for Captures
TCPDUMP is a packet analyzer which displays the transmitted and received packets on the CMX server. It serves as an analysis & troubleshooting tool for Network/System Administrators. The package is built-in to the CMX server where the raw data from the packets can be looked at.
Running tcpdump as 'cmxadmin' user would fail with the following error: ('root' access is required)
In this example, tcpdump is attempted to be run as a 'cmxadmin' user.
[cmxadmin@laughter ~]$ tcpdump -i eth0 port 16113
tcpdump: eth0: You don't have permission to capture on that device
(socket: Operation not permitted)
Switch to 'root' user after logging in as 'cmxadmin' user to the CLI over SSH or console.
[cmxadmin@laughter ~]$ su - root
Password:
[root@laughter ~]#
Using the right interface
Make note of the interface where the packets would be captured. It can be obtained using the 'ifconfig -a'
In this example, 10.10.10.25 is the IP address of CMX server and 'eth0' is the interface it's tied to on the server.
[cmxadmin@laughter ~]$ ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:50:56:A1:38:BB
inet addr:10.10.10.25 Bcast:10.10.10.255 Mask:255.255.255.0
inet6 addr: 2003:a04::250:56ff:fea1:38bb/64 Scope:Global
inet6 addr: fe80::250:56ff:fea1:38bb/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:32593118 errors:0 dropped:0 overruns:0 frame:0
TX packets:3907086 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3423603633 (3.1 GiB) TX bytes:603320575 (575.3 MiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:1136948442 errors:0 dropped:0 overruns:0 frame:0
TX packets:1136948442 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:246702302162 (229.7 GiB) TX bytes:246702302162 (229.7 GiB)
[cmxadmin@laughter ~]$
Capturing packets
This example captures and displays all packets that are sourced from port - 16113 and enter the CMX server on the eth0 interface.
[root@laughter ~]# tcpdump -i eth0 src port 16113
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
09:50:29.530824 IP 172.18.254.249.16113 > laughter.cisco.com.40020: Flags [P.], seq 983381312:983382645, ack 2483597279, win 191, options [nop,nop,TS val 1792647414 ecr 1148435777], length 1333
09:50:31.507118 IP 172.18.254.249.16113 > laughter.cisco.com.40020: Flags [.], seq 1333:2715, ack 1, win 191, options [nop,nop,TS val 1792647908 ecr 1148437650], length 1382
09:50:31.507186 IP 172.18.254.249.16113 > laughter.cisco.com.40020: Flags [P.], seq 2715:2890, ack 1, win 191, options [nop,nop,TS val 1792647908 ecr 1148437650], length 175
09:50:33.483166 IP 172.18.254.249.16113 > laughter.cisco.com.40020: Flags [P.], seq 2890:4239, ack 1, win 191, options [nop,nop,TS val 1792648402 ecr 1148439626], length 1349
09:50:35.459584 IP 172.18.254.249.16113 > laughter.cisco.com.40020: Flags [P.], seq 4239:5396, ack 1, win 191, options [nop,nop,TS val 1792648896 ecr 1148441603], length 1157
^C
5 packets captured
5 packets received by filter
0 packets dropped by kernel
[root@laughter ~]#
To write the Output to a file
In this example, tcpdump would capture packets that are from 10.10.20.5 received on it's eth0 interface and write it to a file named TEST_NMSP_WLC.pcap.
[root@laughter cmxadmin]# tcpdump -i eth0 src 10.10.20.5 -w TEST_NMSP_WLC.pcap
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
^C7 packets captured
7 packets received by filter
0 packets dropped by kernel
[root@laughter cmxadmin]#
Once the file is ready, you will need to extract the .pcap file from the CMX to your computer for analysis in a more comfortable tool such as wireshark. You can use any SCP application to do so. For example in Windows, the WinSCP application will allow you to connect to the CMX using the SSH credentials and you can then browse the file system and find the .pcap file you just created. To find the current path, type "pwd" after running the tcpdump to know where the file was saved.
To Capture specific number of packets
If a specific number of packet count is desired, using the -c option filters exactly for that count.
[root@laughter ~]# tcpdump -Z root -i eth0 -c 5 src 10.10.20.5 -w CMX_WLC_Capture.pcap
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
5 packets captured
6 packets received by filter
0 packets dropped by kernel
[root@laughter ~]#
Other Filtering Options
[root@laughter cmxadmin]# tcpdump -i eth0 dst 10.10.20.5 (filtered based on destination IP address)
[root@laughter cmxadmin]# tcpdump -i eth0 src 10.10.20.4 (filtered based on Source IP address)
[root@laughter cmxadmin]# tcpdump -i eth0 port 80 (filtered for packets on port 80 in both directions)
[root@laughter cmxadmin]# tcpdump -i eth0 port 443 (filtered for packets on port 443 in both directions)
The Captures written to files would be saved in the current directory on the server and can be copied out for detailed review using Wireshark.
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