JUNOS Enterprise Switching

EX to Catalyst VLAN Integration

Having once again muddled our way through the boring background, it’s time to jump on the test bed and put all this information to use. Figure 5-4 details the test topology used in the VLAN trunking integration task.

Before going any further, the following topology characteristics should be duly noted:

• There is a mix of IOS and Juniper EX devices; note that integration is fun.

• The switches and links are chosen to be loop-free and STP is disabled; STP is detailed in the next chapter.

• All switches are running a factory-default configuration with regard to Layer 2 interfaces, with the exception that STP is explicitly disabled.

• The four host machines share an IP subnet that permits full connectivity if allowed by the switched backbone.

Disabling STP in a Switched Network! Are You Crazy?

In a word, yes. That being said, STP serves a useful purpose in a switched Layer 2 network, and failing to run it when it’s actually needed will quickly generate a deluge of flooded traffic that will crash your network. Loops are bad: very, very bad. But so too is running with a pair of scissors, usually.

In this case, we have specific pedagogical reasons for doing this. Chief among them is that STP is covered in the next chapter, it’s not technically needed in a physically loop-free network, and it has little to do with the topics of VLAN tagging and trunking proper. Given that this is not a production network and the topology is known to be loop-free, and considering the flow ...