Category: Switching

Cisco switching

Port-Channel in NX-OS: Let’s Bundle Up!

I am pretty exhausted after having a great NYE. It’s the third week of January but it feels like I need six months of hibernation after 1 night of celebration. If you are feeling the same way, well, we definitely meet up because we’re a good fit for each other. We’re compatible! Let’s be friends!


The topic I like to discuss today is about port-channel in Nexus. Port-channel bundles physical links to form one logical link by using the channel group that provides aggregated bandwidth and redundancy. On the M-series module, you can bundle up 8 physical links but with the release of Cisco NX-OS 5.1, you can bundle up to 16 ports on the F series module. The Port-channel feature does not need a license in order for you to use it. However, since you are going to use VDCs, you need to have the Advanced Services license. This need to be installed before you configure ports within the VDC. Make sure that all member ports are in the same VDC. You can have them configured in any desired VDC but if you are going to configure the load balancing, you must do it in the default VDC. (more…)

VLAN Trunking Protocol (VTP) in Nexus NX-OS – Slight Difference with IOS

VLAN Trunking Protocol (VTP) is also available in Nexus NX-OS. The creation, modification and deletion of VLAN are easy with the use of VTP. Like in the Cisco Catalyst switches, the configuration is just the same. There is not much difference when configuring it but there are some few things to take note. These things make it unlikeable to deploy VTP in a data center environment.

Firstly, let’s discuss VTP version 3. Do you recall what is VTP version 3? Ok, this is the 3rd version of VTP. So what’s the difference with this new version compare to old versions? VTP version 1 and 2 only support a normal range of VLANs from 1 – 1005 but VTP version 3 expands the VLAN range up to 4094. Yes, it is supporting the entire VLAN range! It also supports enhanced authentication where you can configure the password as hidden or secret. VTP version 3 also supports MST and transfer information of private VLANs. Not only that, there is primary server and secondary server concept here where the primary server is responsible for updating and sending updates to VLANs while secondary server serves as a backup. Interesting right? However, in Cisco NX-OS there is no VTP version 3. Yeah, after giving you a lot of exciting features, you cannot use it in Nexus. (more…)

The OSPF Area Types

OSPF Area Types
OSPF Area Types

According to Cisco, OSPF area is a collection of logical OSPF networks (routers and links) that have the same area identification. Depending upon the design of your network, your routers can be part of a single area or multiple areas. Why do we have to complex things and put the router in different areas? Actually, there are many reasons, and one of the many reasons is that it reduces the size of OSPF database when OSPF network is divided into different areas. Think of it this way, dividing the routers into different areas, reduces the size of the database, reduces the frequency of SPF calculation and smaller routing table. Thus, fewer requirements on router memory and CPU. I am not saying that SPF calculation is exhausting the CPU and router memory but the sending and flooding of the new topology information does.

IGP: Open Shortest Path First (OSPF) Overview

EIGRP already has what it takes to be the best IGP. However, there is a need of open standard protocol with fast convergence and supports large enterprise networks. Here comes the Open Shortest Path First (OSPF). OSPF is a link-state routing protocol and uses the Dijkstra’s algorithm (SPF) in finding the shortest path in the network. The OSPF process is a bit complex and understanding the algorithm itself is very intricate. I don’t want to elaborate it piece by piece as I’m afraid if I’m going to be serious about understanding the formula of the algorithm, I might discover a new one which would replace OSPF. No, I’m just joking.