Configuring a Routed Interface

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Dec 1st, 2007
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I woul dliek to create a baseline (standard) for configuring routed physical and virtual interfaces. You know, disabling certain services by default...

I have TWO questions, please:

1. Does the following dialogue make sense? Am I missing something?

With regard to a baseline configuration, routed physical interfaces can be treated the same as Switched Virtual Interfaces (SVI), since they both share many of the same security vulnerabilities and operational characteristics.

Router(config)# interface type [slot/port]

(interface can be Ethernet, serial or vlan)

Router(config-if)# no ip proxy-arp

(disables default proxy-arp behavior)

Router(config-if)# no ip redirect

(disables icmp redirects when default router is down. Use this with HSRP setup)

Router(config-if)# no ip unreachable

(disables icmp unreachable messages in response to icmp echos)

Router(config-if)# no ip directed-broadcast

(applications don't use this anymore. Disable to prevent broadcast storms during a DoS attack)

Router(config-if)# shutdown

(shut down unused interfaces. Otherwise, issue the no shut command to enable)

2. In the event that subinterfaces are being used, do you apply these commands to the physical/main interface or the subinterfaces?


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nambi_gct Sat, 12/01/2007 - 08:39
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1) You are right.

2) You need to apply the commands to the subinterface.

Edison Ortiz Sat, 12/01/2007 - 09:39
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You may want to add

no ip mask-reply

"ICMP mask reply messages can give an attacker the subnet mask for a particular subnetwork in the internetwork."


I'm assuming you are talking about subinterfaces in a router. Generally, you don't create subinterfaces in a switch.

In a router, you should configure all these commands wherever you have IP enabled.

Also, if the device is facing the outside, you may want to disable cdp on that interface no cdp enable


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