Prescriptive Topology Manager
Complex Topology and Wiring Validation in Data Centers describes how Cumulus Networks' prescriptive topology manager (PTM) provides a simple method of verifying and enforcing correct wiring topologies.The following REST call converts the topology from PTM's dot notation and returns a JSON representation:
cumulus@wbench:~$ curl http://leaf1:8080/ptmReturns the result:
{
"links": {
"L1": {
"node1": "leaf1",
"node2": "spine1",
"port1": "swp1s0",
"port2": "swp49"
},
...
}
}
LLDP
Prescriptive Topology Manager is preferred since it ensures that the discovered topology is correct. However, PTM builds on basic Link Level Discovery Protocol (LLDP), which provides an alternative method of topology discovery.The following REST call return the hostname:
cumulus@wbench:~$ curl http://leaf1:8080/hostnameReturns result:
"leaf1"The following REST call returns LLDP neighbor information:
cumulus@wbench:~$ curl http://leaf1:8080/lldp/neighbors
Returns result:
{
"lldp": [
{
"interface": [
{
"name": "eth0",
"via": "LLDP",
"chassis": [
{
"id": [
{
"type": "mac",
"value": "6c:64:1a:00:2e:7f"
}
],
"name": [
{
"value": "colo-tor-3"
}
]
}
],
"port": [
{
"id": [
{
"type": "ifname",
"value": "swp10"
}
],
"descr": [
{
"value": "swp10"
}
]
}
]
},
...
}
]
}
The following REST call returns LLDP configuration information:cumulus@wbench:~$ curl http://leaf1:8080/lldp/configurationReturns result:
{
"configuration": [
{
"config": [
{
"tx-delay": [
{
"value": "30"
}
],
...
}
]
}
]
}
Topology discovery with LLDP
The script lldp.py extracts LLDP data from all the switches in the network and compiles a topology:#!/usr/bin/env python
import sys, re, fileinput, json, requests
switch_list = ['leaf1','leaf2','spine1','spine2']
l = 0
linkdb = {}
links = {}
for switch_name in switch_list:
# verify that lldp configuration exports hostname,ifname information
r = requests.get("http://%s:8080/lldp/configuration" % (switch_name));
if r.status_code != 200: continue
config = r.json()
lldp_hostname = config['configuration'][0]['config'][0]['hostname'][0]['value']
if lldp_hostname != '(none)': continue
lldp_porttype = config['configuration'][0]['config'][0]['lldp_portid-type'][0]['value']
if lldp_porttype != 'ifname': continue
# local hostname
r = requests.get("http://%s:8080/hostname" % (switch_name));
if r.status_code != 200: continue
host = r.json()
# get neighbors
r = requests.get("http://%s:8080/lldp/neighbors" % (switch_name));
if r.status_code != 200: continue
neighbors = r.json()
interfaces = neighbors['lldp'][0]['interface']
for i in interfaces:
# local port name
port = i['name']
# neighboring hostname
nhost = i['chassis'][0]['name'][0]['value']
# neighboring port name
nport = i['port'][0]['descr'][0]['value']
if not host or not port or not nhost or not nport: continue
if host < nhost:
link = {'node1':host,'port1':port,'node2':nhost,'port2':nport}
else:
link = {'node1':nhost,'port1':nport,'node2':host,'port2':port}
keystr = "%s %s -- %s %s" % (link['node1'],link['port1'],link['node2'],link['port2'])
if keystr in linkdb:
# check consistency
prev = linkdb[keystr]
if (link['node1'] != prev['node1']
or link['port1'] != prev['port1']
or link['node2'] != prev['node2']
or link['port2'] != prev['port2']): raise Exception('Mismatched LLDP', keystr)
else:
linkdb[keystr] = link
linkname = 'L%d' % (l)
links[linkname] = link
l += 1
top = {'links':links}
print json.dumps(top,sort_keys=True, indent=1)
Returns result:cumulus@wbench:~$ ./lldp.py
{
"links": {
"L0": {
"node1": "colo-tor-3",
"node2": "leaf1",
"port1": "swp10",
"port2": "eth0"
},
...
}
}
The lldp.py script and the latest version of acl_server can be found on Github, https://github.com/pphaal/acl_server/Demonstration
The acl_server and sFlow agents are installed on the leaf1, leaf2, spine1, and spine2 switches. By default, the sFlow agents automatically pick up their settings using DNS Service Discovery (DNS-SD). Adding the following entry in the wbench DNS server zone file, /etc/bind/zones/lab.local.zone, enables sFlow on the switches and directs measurements to the wbench host:
_sflow._udp 30 SRV 0 0 6343 wbenchNote: For more information on running sFlow in the Cumulus workbench, see Demo: Monitoring Traffic on Cumulus Switches with sFlow). Another point to note, this workbench setup demonstrates the visibility into Link Aggregation (LAG) provides by sFlow (see Link aggregation).
Fabric View is installed on wbench and is configured with the network topology obtained from acl_server. The web interface is accessed through the workbench reverse proxy, but access is also possible using a VPN (see Setting up OpenVPN on the Cumulus Workbench).
This workbench example automatically provisions an OpenStack cluster on the two servers along with the network to connect them. In much the same way OpenStack provides access to virtual resources, Cumulus' Remote Lab leverages the automation capabilities of open hardware to provide multi-tenant access to physical servers and networks.Finally, Cumulus Linux runs on open switch hardware from Agema, Dell, Edge-Core, Penguin Computing, Quanta. In addition, Hewlett-Packard recently announced that they will soon be selling a new line of open network switches built by Accton Technologies and support Cumulus Linux. This article, demonstrates the flexibility that open networking offers to developers and network administrators. If you are curious, its very easy to give Cumulus Linux a try.
