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Forum Replies

  1. Hello James!

    If you have an MTU of 1500 set on a port, then any frame that attempts to ingress on this port that is larger than 1500 bytes will be dropped. If the port is set up to accept larger frames, then it will accept them. As for the FCS, if a frame is smaller than the MTU size that has been configured (either jumbo or not) it will be dropped if the FCS fails regardless of size.

    Note that the DF bit is on the Network Layer, that is, in the IP header. This bit tells the SENDER weather or not the IP packet can be fragmented during encapsulation. Let’s s

    ... Continue reading in our forum

  2. Hello Azm

    This depends on the platform. On the 3750 for example, the MTU cannot be changed on an individual interface, but is implemented globally. On the higher end catalyst switches (4500, 6800 etc) and always depending on the supervisor and IOS used, you can configure it on a per interface basis. In either case, you can verify the MTU on aper interface basis by using

    ... Continue reading in our forum

  3. How do you tell the last time a Cisco Interface flapped?

    Working at ISP I would say a majority is Juniper on a Juniper it actually has “Last Flapped” gives date and time. This is very useful because customer often ask for RFO (reason for outage) You can check interfaces to see last time it flapped. Then you can drill down into logs for the actual reason.

    I was surprised not to find something like this for Cisco?

  4. Hello Brian

    Take a look at this search results page of lessons on the site:


    It gives a list of several topics concerning syslog for both IOS devices as well as ASA firewalls. You might find some additional helpful information there.

    Thanks for sharing the last flap command on the ASR 9000 series devices, it’s good to know.

    As you get more familiar with Cisco, please share with us your thoughts concerning how Cisco compares with Juniper, Alcatel and other vendor devices as far as ease of configuration and use goes, it would

    ... Continue reading in our forum

  5. Thanks Rene. The 8-bit value explanation makes sense.

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