Wassim

In this post, I expose some of my notes about Vlan Trunking Protocol (VTP) on Cisco gear. VTP and Pruning VLAN 1 is not eligible for pruning. So when you try to prune it manually on a switch, you get the following IOS error message: VLAN 1 does not appear on the list of VTP pruned VLANs by the way: Only on the VTP server can we set the “vtp pruning” command, which will propagate to VTP clients only. With it you do not need to configure VTP pruning manually on VTP clients. you can not add a list of pruning vlans in the same row, like you do in adding allowed vlans: to see which VLANs are eligible to be VTP pruned: “show interface {trunk int} switchport”: VTP Modes if there are extended VLANs on a switch, it can not neither be in VTP client nor in server mode. IOS will simply return an error message: the opposite: you can not create extended VLANs while the switch is in VTP server or client mode:

Here are a couple of notes I gathered around the subject of Cisco Etherchannel. We start by some concepts then learn how to configure L3 Etherchannels. Etherchannel concepts EtherChannel is a technology that allows a set of ports to be bundled into one logical interface. There is the logical port (the bundle) and one or more physical ports that constitute it. The physical ports are also called member ports . When one member port fails, traffic that was flowing through it gets redirected over the remaining operational member ports, transparently to the end user and without the network administrator intervention. A physical port can be a member of only one Etherchannel. We can configure an Etherchannel between a network device and a router, a switch, a server,… An EtherChannel can be: a Fast EtherChannel: an EtherChannel formed from Fast Ethernet interfaces a Giga EtherChannel: an EtherChannel formed from Gigabit Ethernet interfaces a port Channel: a layer 3 EtherChannel A port chan...

Here are a couple of commands for viewing and troubleshooting CEF. Cisco Express Forwarding Commands By default, Cisco Express Forwarding and Fast Switching are enabled. (config-if)# no ip route-cache This command disables both Fast Switching and CEF. (config-if)# ip route-cache This command enables Fast Switching only. Cisco Express Forwarding is still disabled if we don’t activate it. (config-if)# ip route-cache cef activates Cisco Express Forwarding under the interface # show platform tcam utilization displays TCAM limits and actual utilization # debug ip cef table This command monitors changes on the Cisco Express Forwarding adjacency table. Let’s run the debug command on a multilayer switch: We list ARP entries: If we remove one entry from ARP table with  clear ip arp  {IP address}: We can see that there’s a change in the Cisco Express Forwarding adjacency table. Indeed, there...

In this short port we explore the possible DTP modes and configure them on a Catalyst switch. We also learn what the outcome would be if we combine them. When configuring the Dynamic Trunking Protocol, Cisco recommends to set trunking as static. But here is the behaviour if we don’t set it to “switchport mode trunk”. For Catalyst 2960 and Catalyst 3560, I found that the default Dynamic Trunking Protocol mode is “dynamic auto”. Key behaviours: Dynamic auto+ dynamic auto = access dynamic auto+ access/trunk = access/trunk Dynamic desirable + access = access Dynamic desirable + else = trunk Default modes Here are a couple of outputs that reveal the default Dynamic Trunking Protocol modes, on Catalyst 2960 and Catalyst 3560: on Catalyst 2960 on a 3560 A combination of the above I’m going to set different DTP modes on both ends of the link, and see the behaviour of DTP on Catalyst switches. I have SW1 and SW0. Dynamic desirable + Access –> Access W...

In this lab, I learned the following: configuring a HSRP group on physical interfaces, testing how a PC can reach a remote subnet through a redundant gateway, by configuring its default gateway as the HSRP virtual address, testing how the second router becomes Active, testing interface tracking. For interface tracking, at first, I thought there was a problem with the lab. Topology: configure interface tracking and a decrement value: When I shut down ser0/0 on R2, I expected R2 to become Standby router. But reality bites: Then I checked on R3. R3 is still Standby, not Active ! So what’s wrong? Here’s what Cisco says: How Object Tracking Affects the Priority of an HSRP Router The priority of a device can change dynamically if it has been configured for object tracking and the object that is being tracked goes down. The tracking process periodically polls the tracked objects and notes any change of value. The changes in the tracked object are communicated to HSRP, either immedi...

I had the opportunity to participate in an official Juniper Networks course titled “Configuring Juniper Networks Routers”, aka CJNR. My boss was kind enough to ask my client to give me five days off. Our instructor was JNCIP certified and works at Twine Networks . All I can say is that 5 days aren’t enough. Juniper Networks should reconsider the necessary time for the CJNR course. There is a lot of knowledge to cover. Labs take a considerable amount of time if you want to assimilate the steps and not only do the secretary work of reading the manual and typing the instructions as shown. For example, we didn’t cover the multicast course as we ran out of time. Topics like BGP, routing policies, multicast and firewall filters on JUNOS sounded like “Chinese English” to me.

import = receive into routing table export = send to neighbors, or, redistribute (or not).OSPF —— Default import policy: accept all OSPF routes from neighbors Default export policy: advertise all direct routes (including loopback interfaces).Here’s an example to illustrate it. Dubai learned the 15.15.15.15/32 route through OSPF from Tokyo. In fact, the default export policy in Tokyo is to advertise its direct routes, one of which is 15.15.15.15/32. The default export policy on Dubai is to export all direct routes. Then MontReal learned 15.15.15.15/32 from Dubai, because the default import policy is to accept any OSPF routes. Wait a minute, 15.15.15.15/32 is not a direct route in Dubai. So how does Dubai advertise it to MontReal? I found the answer to it in JUNOS Enterprise Routing book. It says : “ The default LS export policy is to reject everything. LSA flooding is not affected by export policy, and it is used to convey routing in an indirect manner in an LS pr...