Flowtracker Overview
This script enables on demand troubleshooting of a DC fabric running Nexus switches, by taking in a 5-tuple and tracing the path of this flow across the network.
It can be executed on any standalone host with Python installed (e.g. Linux, Mac, or Windows).
It requires the external python libraries, pycsco and netmiko, but these can be installed automatically using the installation instructions below.
Installation
(syntax below for Linux/Mac, but analogous steps for Windows)
via pip:
If your host has pip installed, you can simply do:
sudo pip install flowtracker
by cloning this repository:
git clone https://github.com/networktocode/flowtracker.git
cd flowtracker
sudo python setup.py install
Both methods install an executable on the host's system path so that the script can be executed by simply typing flowtracker from the command prompt.
Usage
Script arguments
The arguments given to the script supply information about the flow to track, and the Nexus switches to contact. All arguments can be supplied either via command line flags, or by interactive prompt to the user. If an argument isn't supplied by a flag, the user will be prompted for that argument. A special flag -h or --help prints a description about each of the other arguments and how to use them as command line flags. Below is the output from running flowtracker -h.
usage: flowtracker [-h] [--src SRC] [--dest DEST] [--proto PROTO]
[--target TARGET] [--user USER] [--pwd PWD]
[--src_port SRC_PORT] [--dest_port DEST_PORT]
[--vrf VRF] [--mode {interactive,auto}] [--use_mgmt]
optional arguments:
-h, --help show this help message and exit
--src SRC The source IP address or hostname of the flow.
--dest DEST The destination IP address or hostname of the flow.
--proto PROTO The IP protocol number. Common names like icmp, tcp,
and udp may be used.
--target TARGET The IP address or hostname of the switch to start the
flow track.
--user USER The SSH/NXAPI username for the switch.
--pwd PWD The SSH/NXAPI password for the switch.
--src_port SRC_PORT The source layer 4 port of the flow.
--dest_port DEST_PORT
The destination layer 4 port of the flow.
--vrf VRF The VRF of the flow.
--mode {interactive,auto}
Interactive mode prompts the user to continue at each
hop.
--use_mgmt Use the Management IP address to connect to each hop.
Uses the NXAPI instead of SSH.
The --mode argument, which can only be supplied as a command line flag, provides two modes to run the script, interactive(default) and auto. interactive will prompt the user to Enter to continue to next hop, at each hop in the path, after printing flow information. auto will automatically move on to each hop.
The --use_mgmt flag, if set, instructs the script to connect to each switch on its management interface. If it is not set, the script uses the next hop IP address, learned at each hop, to connect to the next hop. A side effect of setting this flag is that the script attempts to use NX-API, with SSH as fall back. If the flag isn't set, the script only uses SSH. Using NX-API yields dramatic speed improvements in the running time of the script.
Like most other arguments, if the SSH/NXAPI password (--pwd) isn't supplied via a command line flag, the user is prompted for it. When the user types at the prompt, the password is not displayed on screen. However if --pwd is supplied via command line flag, the password is displayed on screen.
Running the script:
Below is an example runing the script with a combination of command line flags and prompts. --mode, --use_mgmt, --target, and --user are supplied via command line flags. The flow's source IP, destination IP, source port, destination port, IP protocol are supplied by responding to prompts. Likewise are the password, and vrf. The password is hidden, and the optional vrf argument is not supplied, so the "default" vrf will be used.
Initial execution:
flowtracker --mode auto --use_mgmt --target p9372-1 --user cisco
Prompts:
Enter source IP of the flow: 3.3.3.3
Enter destination IP of the flow: 4.4.4.4
Enter IP protocol(tcp, udp, icmp, <number>): tcp
SSH/NXAPI Password:
(Optional) TCP/UDP Source Port: 1234
(Optional) TCP/UDP Destination Port: 80
(Optional) VRF of the flow:
Below is the output of the script given the above input. First a FLOW OVERVIEW is displayed, recapping the inputs given. Then, the output at each hop in the path is displayed and separated by a line of #'s.
At each hop, we see which hop we are CONNECTED TO, its HOP NUMBER, and the LOAD_SHARE_MODE. We also see the outgoing interface of the flow in OUT_IF, and the NEXT_HOP. At the bottom, interface statistics about the OUT_IF are displayed:
FLOW OVERVIEW:
SRC: 3.3.3.3
DEST: 4.4.4.4
PROTO: 6
SRC_PORT: 1234
DEST_PORT: 80
VRF: default
#############################################################################
CONNECTED TO: 9372-1 (p9372-1)
HOP NUMBER: 1
LOAD_SHARE_MODE: address source-destination port source-destination
VRF: default
OUT_IF: Eth1/52
DEST: 4.4.4.4
NEXT_HOP: 10.10.60.1
OUT_IF:
RESETS: 6
TX_STATS:
1552 unicast packets 233683 multicast packets 3 broadcast packets
235246 output packets 24675632 bytes
0 jumbo packets
0 output error 0 collision 0 deferred 0 late collision
0 lost carrier 0 no carrier 0 babble 0 output discard
0 Tx pause
Elapsed Time for Hop: 1.347575 seconds.
#############################################################################
CONNECTED TO: N9K2 (10.10.60.1)
HOP NUMBER: 2
LOAD_SHARE_MODE: address source-destination port source-destination
VRF: default
OUT_IF: Eth2/3
DEST: 4.4.4.4
NEXT_HOP: 10.10.70.2
OUT_IF:
RESETS: 2
TX_STATS:
81 unicast packets 27053 multicast packets 3 broadcast packets
27150 output packets 3490279 bytes
0 jumbo packets
0 output error 0 collision 0 deferred 0 late collision
0 lost carrier 0 no carrier 0 babble 0 output discard
0 Tx pause
Elapsed Time for Hop: 4.153353 seconds.
#############################################################################
CONNECTED TO: 9372-2 (10.10.70.2)
HOP NUMBER: 3
LOAD_SHARE_MODE: address source-destination port source-destination
VRF: default
OUT_IF: sup-eth1 , local, attached
DEST: 4.4.4.4
NEXT_HOP: sup-eth1
OUT_IF:
RESETS: N/A
TX_STATS: N/A
Elapsed Time for Hop: 0.192762 seconds.
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