Mar
30
OSPF and MTU Mismatch Dear Brian, What is the difference between using the “system mtu routing 1500” and the “ip ospf mtu-ignore” commands when running OSPF between a router and a switch? Thanks, Paul Hi Paul, Within the scope of the CCIE Lab Exam, it may be acceptable to issue either of these commands to solve a specific lab task. However, it is key to note that there is a difference between ignoring the MTU for the purpose of OSPF adjacency and matching the MTU within a real production... Read More
Nov
05
Fragmented IPv4 traffic may cause you a lot of problems in real life. Not only it increases the load on router CPUs, but also impacts applications performance (e.g. TCP needs to re-send the whole packet on a single fragment loss). In addition to that, traffic fragmentation is used in numerous network attacks, allowing an attacker to bypass firewalls or IDSes in some situations. Due to all these reasons, you may want to avoid fragmentation at all and/or ensure your network is insulated from... Read More
Jan
20
Below are a couple example configurations for PPPoE. Note that you can run into MTU issues when trying to use OSPF over PPPoE. This can easily be resolved by using the "ip ospf mtu-ignore" command as the dialer interface's MTU is 1492 while the virtual-template's (virtual-access) MTU is 1500. Read More

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