First and foremost, I’m going to assume you have a basic working knowledge of FabricPath, Cisco’s scalable Layer 2 solution that eliminates Spanning Tree Protocol and adds some enhancements that are sorely needed in L2 networks like Time To Live (TTL), Reverse Path Forwarding (RPF) and uses IS-IS as a control plane protocol. It’s the fact that FabricPath uses IS-IS that makes it very easy and familiar for customers to enable authentication in their fabric. If you have ever configured authentication for a routing protocol in Cisco IOS or NX-OS, this will be similar with all of your favorites like key chains, key strings and hashing algorithms. Hopefully that nugget of information doesn’t send you into a tail spin of despair. ;)
With FabricPath there are two levels of authentication that can be enabled.
The first is at the domain level for the entire switch (or VDC!).
Authentication here will prevent routes from being learned. Important to note that
ISIS adjacencies can be formed on the interface level even when the domain authentication
is mismatched. This domain level authentication is for LSP and NSP exchange not
PDUs on the interfaces. If you are not
careful, you can blackhole traffic during the implementation of authentication,
just like you would with any other routing protocol.
A quick order of operation to enable domain level authentication would be
to define a key-chain with keys which contain key-strings defined underneath.
The key strings are the actual password and NX-OS allows you to define multiple
key-strings so you can rotate passwords as needed and even includes nerd knobs
for setting start and end times. After the key chains are defined, they are
applied to the FabricpPath domain. Let’s quit typing and let the CLI do the
talking.
We start with a VDC that has FabricPath, is in a fabric with other devices
but doesn’t have authentication enabled. We can see we have not learned any
routes.
N7K-2-Access2# show fabricpath routeFabricPath Unicast Route Table
'a/b/c' denotes ftag/switch-id/subswitch-id
'[x/y]' denotes [admin distance/metric]
ftag 0 is local ftag
subswitch-id 0 is default subswitch-id
FabricPath Unicast Route Table for Topology-Default
0/4/0, number of next-hops: 0
via ---- , [60/0], 24 day/s 00:32:41, local
0/69/1, number of next-hops: 0
1/69/0, number of next-hops: 0
via ---- , [60/0], 15 day/s 04:18:01, local
2/69/0, number of next-hops: 0
via ---- , [60/0], 15 day/s 04:18:01, local
We can also see we are adjacent to some other devices, but also note that
we *don’t* see their name under system ID, just the MAC address. This is a
quick point that something is amiss with the control plane. They are in bold
and red below.
N7K-2-Access2# show fabricpath isis
adjFabricpath IS-IS domain: default Fabricpath IS-IS adjacency database:
System ID SNPA Level State Hold Time Interface
0026.980f.d9c4 N/A 1 UP 00:00:25 port-channel1
0024.98eb.ff42 N/A 1 UP 00:00:29 Ethernet3/9
0024.98eb.ff42 N/A 1 UP 00:00:27 Ethernet3/10
0026.980f.d9c2 N/A 1 UP 00:00:22 Ethernet3/20
0026.980f.d9c2 N/A 1 UP 00:00:29 Ethernet3/21
Now we’ll add the authentication and start with the key-chain and call it “domain”
then define key 0 and the key-string of “domain” (not very creative am I?) and
then finally apply it to the fabricpath domain default.
N7K-2-Access2# config
Enter configuration commands, one per line. End with CNTL/Z.
N7K-2-Access2(config)# key chain domain
N7K-2-Access2(config-keychain)# key 0
N7K-2-Access2(config-keychain-key)# key-string domain
N7K-2-Access2(config-keychain-key)# fabricpath domain default
N7K-2-Access2(config-fabricpath-isis)# authentication key domain
Now let’s see what that does for us.
Much happier now aren’t we?
N7K-2-Access2(config-fabricpath-isis)#
show fabricpath routeFabricPath Unicast Route Table
'a/b/c' denotes ftag/switch-id/subswitch-id
'[x/y]' denotes [admin distance/metric]
ftag 0 is local ftag
subswitch-id 0 is default subswitch-id
FabricPath Unicast Route Table for Topology-Default
0/4/0, number of next-hops: 0
via ---- , [60/0], 24 day/s 00:33:32, local
0/69/1, number of next-hops: 0
1/1/0, number of next-hops: 2
via Eth3/20, [115/40], 0 day/s 00:00:10, isis_fabricpath-default
via Eth3/21, [115/40], 0 day/s 00:00:10, isis_fabricpath-default
1/2/0, number of next-hops: 2
via Eth3/9, [115/40], 0 day/s 00:00:11, isis_fabricpath-default
via Eth3/10, [115/40], 0 day/s 00:00:11, isis_fabricpath-default
1/69/0, number of next-hops: 0
via ---- , [60/0], 15 day/s 04:18:52, local
1/100/0, number of next-hops: 4
via Eth3/9, [115/40], 0 day/s 00:00:11, isis_fabricpath-default
via Eth3/10, [115/40], 0 day/s 00:00:11, isis_fabricpath-default
via Eth3/20, [115/40], 0 day/s 00:00:10, isis_fabricpath-default
via Eth3/21, [115/40], 0 day/s 00:00:10, isis_fabricpath-default
2/69/0, number of next-hops: 0
via ---- , [60/0], 15 day/s 04:18:52, local
N7K-2-Access2(config-fabricpath-isis)#
The exact same sequence applies to interface-level authentication and looks
like the CLI below. We can see that when we have two non-functioning states
here – INIT and LOST. INIT is from me removing the key-chain and flapping the
interface (shut/no shut) and LOST is from me removing the pre-defined key chain
and the adjacency going down to N7K-1-Agg1.
N7K-2-Access2# show fab
isis adjFabricpath IS-IS domain: default Fabricpath IS-IS adjacency database:
System ID SNPA Level State Hold Time Interface
N7K-1-Access1 N/A 1 UP 00:00:27 port-channel1
N7K-2-Agg2 N/A 1 INIT 00:00:22 Ethernet3/9
N7K-2-Agg2 N/A 1 UP 00:00:23 Ethernet3/10
N7K-1-Agg1 N/A 1 LOST 00:04:57 Ethernet3/20
N7K-1-Agg1 N/A 1 UP 00:00:30 Ethernet3/21
Now we’ll add our key chain and key string.
N7K-2-Access2# config
Enter configuration
commands, one per line. End with CNTL/Z.
N7K-2-Access2(config)#N7K-2-Access2(config-keychain-key)# int e3/9
N7K-2-Access2(config-if)# fabricpath isis authentication-type cleartext
N7K-2-Access2(config-if)# fabricpath isis authentication key-chain interface
N7K-2-Access2(config-if)#
N7K-2-Access2(config-if)# key chain interface
N7K-2-Access2(config-keychain)#key 0
N7K-2-Access2(config-keychain-key)# key-string 7 interface
N7K-2-Access2(config-keychain-key)#
N7K-2-Access2(config-keychain-key)# int e3/9
N7K-2-Access2(config-if)# fabricpath isis authentication-type cleartext
N7K-2-Access2(config-if)# fabricpath isis authentication key-chain interface
N7K-2-Access2(config-if)#
A quick check shows us we’re happily adjacent to our swiches.
N7K-2-Access2(config-keychain)# show fab isis adj
Fabricpath IS-IS domain: default Fabricpath IS-IS adjacency database:System ID SNPA Level State Hold Time Interface
N7K-1-Access1 N/A 1 UP 00:00:30 port-channel1
N7K-2-Agg2 N/A 1 UP 00:00:29 Ethernet3/9
N7K-2-Agg2 N/A 1 UP 00:00:26 Ethernet3/10
N7K-1-Agg1 N/A 1 UP 00:00:24 Ethernet3/20
N7K-1-Agg1 N/A 1 UP 00:00:31 Ethernet3/21
Finally, a quick command to
check the FabricPath authentication status on your device is below:
N7K-2-Access2# show fab isi
Fabricpath IS-IS domain : default
System ID : 0024.98eb.ff43 IS-Type : L1SAP : 432 Queue Handle : 11
Maximum LSP MTU: 1492
Graceful Restart enabled. State: Inactive
Last graceful restart status : none
Metric-style : advertise(wide), accept(wide)
Start-Mode: Complete [Start-type configuration]
Area address(es) :
00
Process is up and running
CIB ID: 3
Interfaces supported by Fabricpath IS-IS :
port-channel1
Ethernet3/9
Ethernet3/10
Ethernet3/20
Ethernet3/21
Level 1
Authentication type: MD5
Authentication keychain: domain Authentication check specified
MT-0 Ref-Bw: 400000
Address family Swid unicast :
Number of interface : 5
Distance : 115
L1 Next SPF: Inactive
N7K-2-Access2#
With this simple exercise you’ve
configured FabricPath authentication. Not too bad and very effective. As always
when configuring passwords on your device, cut and paste from a common text
file is important to avoid empty white spaces at the end of passwords and other
nuances that can lead you down the wrong path. In general, I would expect a
customer who implements FabricPath authentication will probably configure both
domain and interface level authentication.
As always, your comments and
feedback are appreciated!
the domain auth is very confusing. When you enable this on one side only the isis adj look like working but the actual forwarding frame is not working.
ReplyDeleteThanks for this post, was very helpful for me.
Roie