How Virtual Port Channel Avoid Duplicate Frames

There is one critical rule with vPC. If a member port receives a frame, it is forwarded across the peer-link. When the peer switch receives it, it will not forward the frame out a vPC member port. Why does this happen? Have a look at the diagram below.

Frames received on a member port, then forwarded across the peer-link, will not be forwarded out another member port

There are two servers connected by vPC member ports. Server-1 sends a frame to Server-2. The traffic flows like this:

1. The frame travels up the link from Server-1 to Peer-1

2. Peer-1 forwards the frame down the link to Server-2

3. Peer-1 also forwards the frame across the peer-link to Peer-2

4. Peer-2 sees that the frame came from a vPC member port, and refuses to forward it to Server-2

So, why does Peer-2 drop the frame? Peer-1 has already delivered it. If Peer-2 also tried to deliver the frame, server-2 would receive a duplicate frame.

Of course, this does not apply to orphaned ports. They are not multi-homed with vPC, and cannot get duplicate frames.

UPGRADING EOS in the ARISTA Switches

UPGRADING EOS in the ARISTA Switches: EOS is the Firmware for Arista Switches whereas IOS for Cisco. This blog post shows the detailed procedures to follow and to upgrade the EOS in the Arista Switches. This Post was supports for any platform or the Version you are going to upgrade in the Arista Switches. This Post was divided into three parts : Pre-Upgrade Process Upgrade Process Post-Upgrade Process PRE-UPGRADING-PROCESS: 1 1) Check the Upgrade Path tool by clicking the below link. https://www.arista.com/en/support/mlag-portal/mlaglist and confirm it is in mlag issu compatible 2) Check if the STP agent is restartable by giving the command switch-1# show spanning-tree bridge detail | grep agent Stp agent restartable : ...

Destination IP Address of DHCP

When DHCP starts the client has no idea about the network it’s currently on. Some clients may store the IP address they were previously on and send this out with the Discovery and Request packets, but the network is not truly set up until after the server has sent it’s final Ack message. Because of this the server does not know the network’s true broadcast address, however there is an address mapped for this very purpose. 255.255.255.255 If you run arp -a you will see that every interface has the following mapping 255.255.255.255 ff-ff-ff-ff-ff-ff static This means that just like a networks broadcast IP this message will be transmitted to all network adapters on the local network segment. The DHCP server listens for messages heading for port 67 UDP while the DHCP client listens for messages on port 68 UDP Lets lake a look at a DORA sequence in Wireshark 148 16.564069 0.0.0.0 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0xaccba128 149 16.5...

Loadbalancing on Static Routes

If you have two routers / two Layer3 switches connected with two L3 links (two paths) you can route with two equal static routes towards the same prefix and the router will load balance traffic across both links. The idea is to make two same static routes on the same router but with different next-hops. The question was: Which link or which route will be used? And if the traffic will be load balanced, which mechanism will be used to share the traffic across both of links. ip route 10.0.0.0 255.0.0.0 192.168.10.2 ip route 10.0.0.0 255.0.0.0 192.168.11.2 If both routes have the same destination prefix and no different Administrative Distance is configured, both routes will get installed in the routing table. Routing table will then leave to the switching process the job of load-sharing. That is, route-cache mechanisms, CEF in case of Cisco device will do load-share per session using source-destination IP. MORE ABOUT THAT CEF Load-Balancing Overview CEF – Cisco E...

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