We're Sorry, Full Content Access is for Members Only...

If you like to keep on reading, Become a Member Now! Here is Why:

  • Learn any CCNA, CCNP and CCIE R&S Topic. Explained As Simple As Possible.
  • Try for Just $1. The Best Dollar You've Ever Spent on Your Cisco Career!
  • Full Access to our 638 Lessons. More Lessons Added Every Week!
  • Content created by Rene Molenaar (CCIE #41726)

 

365 New Members signed up the last 30 days!

satisfaction-guaranteed

100% Satisfaction Guaranteed!
You may cancel your monthly membership at any time.
No Questions Asked!

Tags: ,


Forum Replies

  1. Hi Yevgeniy,

    DHCP Option 82 stands for “DHCP Relay Agent Information Option”. If you haven’t seen how DHCP relay works before, take a look at this lesson:

    https://networklessons.com/cisco/ccie-routing-switching/cisco-ios-dhcp-relay-agent/

    Option 82 was originally created for really large (WAN) networks where we have a lot of DHCP relays and central DHCP servers. The idea behind it is that the DHCP relay can add extra information which the DHCP server can use to decide which pool to use for assigning an IP address. Option 82 has a “Circuit ID” and a “Remote ID”

    ... Continue reading in our forum

  2. Hi Bishoy,

    We only configure interfaces as trusted if the interface is connected to an DHCP server or if it’s an uplink towards the DHCP server.

    If you would configure the fa0/1 interface as trusted, the client could run a fake DHCP server which is exactly what we are trying to prevent here :slight_smile:

    Rene

  3. Zaman,
    IOS XE is a different from the “traditional” IOS operating system in terms of its architecture. IOS XE still runs the traditional IOS, but it runs as a single process (daemon) within a larger linux operating system. Notice in your output, there is an indication of this (linux):

    (X86_64_LINUX_IOSD-UNIVERSALK9-M)

    So, “Version 03.12.00a.S” refers to the large linux operating system, while “Version 15.4(2)S0a” refers to the IOS version being run by the IOS daemon within IOS XE. Make sense?

    Here’s some more info on IOS XE if you want to read about the new

    ... Continue reading in our forum

  4. Hello Manuel

    Rene describes what option 82 does in this post very well.

    As to why you should disable option 82, when DHCP snooping is enabled on a switch, option 82 is enabled by default. That is, any DHCP request packets that are sent from a host will enter the switch and will have option 82 information ADDED to the request before it is sent on to the DHCP server. Specifically, enabling DHCP snooping on the switch adds the giaddr value of 0.0.0.0 in the DHCP packet. However, the DHCP server is expecting this field to be set to that of the relay agent (a non

    ... Continue reading in our forum

  5. Hello Harry

    When you post a question, try to find a thread that is close to the topic that you are asking about. This is the perfect thread for this question. However, if you find that there is no thread that matches your question, you can always post a new topic, and we may re-categorize it into the appropriate thread.

    As for your question, keep in mind that the IP helper address command installed on the local router will just take any DHCP request that it hears on the network and forward it to the DHCP server that exists on a different subnet. This does no

    ... Continue reading in our forum

18 more replies! Ask a question or join the discussion by visiting our Community Forum