Loopback interface

Answered Question
Sep 10th, 2007
User Badges:

I am using EIGRP as the routing protocol to my network. The previous guy has enable loopback interface in each router and layer 3 switches and assigned to each an ip address.

Do i really need the loopback interface and what's the use?

If i really need that what ip address should i use(for examble should i use a mask /29 for wan links and assign three ip addresses, two wan ip and one loopback or use onother different ip )?

Thanks

moses

Correct Answer by Richard Burts about 9 years 9 months ago

Moses


While not generally required, a loopback interface can be very useful and is frequently configured to assist in management functions. It might make accessing the router more easy (especially when there are multiple interfaces and multiple addresses) to have a single address that will work as long as at least one of those interfaces is up and active. Also for network management we frequently want all system messages (syslog messages, SNMP messages, etc) to come from the same address. In configuring AAA authentication or authorization we frequently want to specify a source address for the authentication or authorization packets and use a loopback. Sometimes we might want to specify a source address for telnet, for TFTP or FTP, for SSH, for NTP, or for some other functions. To use the loopback address for any of these purposes it must be routable which means that there needs to be an EIGRP network statement that includes the loopback address.


If you use a loopback interface address you certainly would not want it to be in the subnet of your serial interface. It should have its own subnet. Frequently people configure loopback interfaces with a /32 mask. But the loopback address can be configured with any legitimate subnet mask.


HTH


Rick

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Loading.
Correct Answer
Richard Burts Mon, 09/10/2007 - 06:43
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN

Moses


While not generally required, a loopback interface can be very useful and is frequently configured to assist in management functions. It might make accessing the router more easy (especially when there are multiple interfaces and multiple addresses) to have a single address that will work as long as at least one of those interfaces is up and active. Also for network management we frequently want all system messages (syslog messages, SNMP messages, etc) to come from the same address. In configuring AAA authentication or authorization we frequently want to specify a source address for the authentication or authorization packets and use a loopback. Sometimes we might want to specify a source address for telnet, for TFTP or FTP, for SSH, for NTP, or for some other functions. To use the loopback address for any of these purposes it must be routable which means that there needs to be an EIGRP network statement that includes the loopback address.


If you use a loopback interface address you certainly would not want it to be in the subnet of your serial interface. It should have its own subnet. Frequently people configure loopback interfaces with a /32 mask. But the loopback address can be configured with any legitimate subnet mask.


HTH


Rick

Actions

This Discussion