Interior Gateway Protocols (IGPs)

IGPs are used for routing within an autonomous system (AS) or an internal network. They help routers exchange routing information and make routing decisions within the boundaries of the AS. Some common IGPs include Routing Information Protocol (RIP), Open Shortest Path First (OSPF), and Intermediate System to Intermediate System (IS-IS). IGPs are typically used to facilitate communication and routing between routers within a single organization or network.

Key characteristics of IGPs:

1. Used for routing within a single autonomous system or internal network.
2. Exchange routing information between routers within the same network domain.
3. Typically focus on factors such as shortest path or link cost when making routing decisions.
4. Examples include RIP, OSPF, IS-IS.

Exterior Gateway Protocols (EGPs):

EGPs, on the other hand, are used for routing between autonomous systems (ASes) or different networks operated by separate organizations. Their primary purpose is to exchange routing information between different ASes on the internet. The most widely used EGP is the Border Gateway Protocol (BGP), which enables routers to exchange routing information across multiple networks and make routing decisions that span across AS boundaries.

Key characteristics of EGPs:

1. Used for routing between autonomous systems or different networks.
2. Exchange routing information between routers in different ASes.
3. Focus on factors such as AS path, policies, and external reachability when making routing decisions.
4. Examples include Border Gateway Protocol (BGP).

In summary, IGPs are employed for internal routing within a network or autonomous system, while EGPs are used for routing between autonomous systems or different networks. The scope, routing decision factors, and the protocols used are the primary distinctions between these two types of gateway protocols.

Yeah!

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.

Though they always said that it’s not good to compare, it’s not true in the networking technology or maybe in other technologies not only in the network world. We always compare. Like in IOS, NX-OS requires all the members of port-channel to have compatible parameters. Else, the port-channel will not form.

So, the first thing that you need to do is to verify whether the following parameters are the same for all member ports:

• port mode
• speed
• MTU
• shut lan
• MEDIUM
• span mode
• load interval
• Access VLAN, Trunk native VLAN, and Allowed VLAN list
• 802.3x flow control setting

How do you do that? Use the “show port-channel compatibility-parameters” command. We will discuss more of it in my future port-channel lab post.

Another thing that is important to take note is that Cisco NX-OS does not support PAgP. The Cisco proprietary Port Aggregation Protocol (PAgP) is not supported for some reasons.

PORT-CHANNEL TOPICS:

• Default Port-Channel Parameters
• Port-Channel Basic Settings
• Configuring Port-Channel
• Port-Channel Load Balancing
• Port Channel Verification

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.

There is, however, another limitation. IOS VTP pruning is only good for normal VLAN range but in Nexus 5K (Nx5K), it does not support VTP pruning at all.

In NX-OS, the default mode is disabled. Like the routing protocols that need to be enabled manually, you also need to manually enable VTP using the “feature vtp” command. Moreover, NX-OS supports VTP mode off. Off mode behaves like transparent mode but it does not forward VTP packets on trunks.

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.

OSPF AREA TYPES

No matter what your OSPF design in your network, all areas you have created should be connected to the backbone area. Backbone area or Area 0 (0.0.0.0) is like the meeting points of all these non-backbone areas. So, it is not just an option or recommendation but a must in every OSPF network design. Although there is an option called virtual link, it is not a good network design but just a remedy to a broken OSPF design.

Now, not all LSA Types are allowed in different areas. Some LSA Types are restricted and depend upon which area type is configured. This further reduces the link state database and routing tables. Injecting too many external routes are also memory intensive. However, all LSA types are allowed in the Normal area. An area which is not configured as Stub, Totally Stub, NSSA, NSSA Totally Stub area is called Standard/Normal Area. We can say that the backbone area is behaving like a Normal /Standard Area as LSA Type 1-5 are not being restricted in this area. When the network is divided into different area numbers (non-zero), an ABR is used to connect the Standard area to the Backbone Area.

On my next post, I will introduce some of the area types which have their own rules in restricting LSA Types.