Recently in Routing Category

I just stumbled across this killer post on Shawn's Blog that describes how to set up IP SLA to allow a static route to failover if pings to a specified internet host should fail. This is really useful if you have two ISPs (and thus, two default routes) where the router cannot detect a link failure. This is really common if you have a cable/DSL modem or some type of wireless connectivity. Here's the basic config, taken directly from Shawn's Blog:

ip sla 1 < The number 1 here is arbitrary, used only to identify this sla. It is otherwise knows as the operation number>

icmp-echo 4.2.2.2 < 4.2.2.2 is a DNS server that responds to pings out on the internet>

timeout 500 < This is how long to wait for a response from the ping>

frequency 3 < This is the repeat rate for the SLA>

ip sla schedule 1 start-time now life forever < This command says "start SLA 1 now and keep it running forever>

track 1 rtr 1 reachability < This comand creates the track object "1" and monitors the SLA 1>

now for the routing, we need to change the default route and associate it with the tracker

no ip route 0.0.0.0 0.0.0.0 1.1.1.1

and then put it back with the tracking

ip route 0.0.0.0 0.0.0.0 1.1.1.1 track 1

Then we need to add our secondary route

ip route 0.0.0.0 0.0.0.0 1.1.1.2 10

Now when the ping to 4.2.2.2 fails the primary route is removed and the secondary route with the higher metric becomes the default. The route will be reinstated when the connectivity is restored.

With the 12.4 and higher releases the commands have changed slightly but the "?" is your friend. If I receive requests for the syntax I will post it as well, but it is pretty easy to convert.

Here is the reference to the Cisco IP SLA documentation

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a0080441845.html

In the consulting world, I get this request all the time: "I've got two ISPs with equal bandwidth connections for redundancy. Can I load balance between them?" Well, Cisco just published an article addressing exactly this. Check out the link below - it provides a configuration that uses features such as SLA to ping remote devices and make sure they are online before using a specific interface. There were some interface tracking features in here that I didn't even know existed! Nice!!!

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_configuration_example09186a00808d2b72.shtml

UPDATE: NIL just published a guide on Load Balancing using BGP, also pretty sweet.

I stumbled on this router while reading through some new Cisco marketing mish-mesh...Alright - check this thing out: it's a branch router that does...EVERYTHING!

CallManager / Unity Express (VoIP Phones)
VPN Support (site-to-site, remote access, SSL VPNs)
Firewall features
802.1x features
HWIC Slot (for WAN cards)
Built in FXS/FXO slots (for POTS phones & phone lines)

The only thing it's missing is wireless...but still sweet nonetheless. It's so new, I can't find out how much it costs yet...I'm guessing 2,000 - 3,000 dollars...donations anyone?

These guys at NIL continue to impress me. I originally met one of the NIL staff when I was running a BGP lab at Cisco Networkers a couple years back. We sat and talked about regular expressions with each other while the Networkers folks hacked away at the remote NIL equipment. Ever since then, I've glanced at their website from time to time - they just added a great post on migrating routing protocols:

http://www.nil.com/go/ChangingRoutingProtocol/

While you're there, you can find a wealth of other "best practice/cool tips" articles they have on-hand. This was the first place I learned about the Configure Replace command...which I've found doesn't work as well in practice as it does in theory. But that's another post :).

TCP/IPv6 is going to reshape the networking world completely. We all know "it's coming" (insert creepy music here), but no one really wants to learn it. So, what I tried to do is record video that was simple enough to follow, yet technical enough to give you some practical information to take away. My good friends over at CBTNuggets have agreed to allow me to reproduce that video here at no cost to you. It's from the new Cisco BSCI series. Enjoy!

Click here to download (Microsoft WMV format)

One of the most common questions I get from new Cisco folks is, "how do I configure NAT on a Cisco router?" Rather than just explain it, I thought I'd show ya :o).

Click here to check it out!

Please let me know what you think.

This last week, I ended up doing a basic deployment over at the AT&T NOC here in Mesa, Arizona. There's nothing like the feeling of walking into a NOC, complete with full hand scanners that also check for a pulse equipping each door, hundreds of racks of equipment, the fan whir so loud that you can't hear yourself think. Ah, I'm slipping back into it just thinking about it.

Back to the topic at hand: the client had dual routers connected to AT&T in the configuration below:

This redundant topology just begged to use one of the redundancy protocols: HSRP, VRRP, or GLBP. The big question is...which one? ...and why? Well, me being a Cisco spud, I immediately gravitated to HSRP since that's all I know very well. But before I left, I decided to check out the competition, here's what I found:

Cisco Hot-Standby Router Protocol (HSRP):

• Created by Cisco, for Cisco in 1994
  
• Uses a default hello timer of 3 seconds with a hold timer of 10 seconds

Virtual Router Redundancy Protocol (VRRP)

• Created by the IETF in 1999
  
• Works between multiple vendors
  
• Has faster timers than HSRP by default - hello of 1 second, hold timer of 3 seconds

Gateway Load Balancing Protocol (GLBP)

• Created by Cisco, for Cisco in 2005
  
• Identical features to HSRP, but allows an active-active connection that adds load-balancing features

Since this client had no need for load balancing, I decided to go with the VRRP option. The configuration was a piece of cake:

Router1(config-if)#vrrp 1 ip 10.1.6.1 (they obviously used a real IP address)
Router1(config-if)#vrrp 1 preempt
Router1(config-if)#vrrp 1 priority 100

Router2(config-if)#vrrp 1 ip 10.1.6.1
Router2(config-if)#vrrp 1 preempt
Router2(config-if)#vrrp 1 priority 120

This is what the end topology looked like. Obviously, I've removed the IP addresses to protect the innocent :).

I've also included links to the full Cisco documentation for each of these protocols.

Cisco HSRP
Cisco GLBP
IETF VRRP