ABOUT NETWORKING

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 Express Fo

We are going back to networking basics with this post. In few lines below you will find most important theory that makes network gear do its job. The main router job is to making routing decisions to be able to route packets toward their destination. Sometimes that includes recursive lookup of routing table if the next-hop value is not available via connected interface. ROUTING DECISION ON END DEVICES Lets have a look at routing decision that happens if we presume that we have a PC connected on our Ethernet network. If one device wants to send a packet to another device, it first needs to find an answer to these questions: Is maybe the destination IP address chunk of local subnet IP range? If that is true, packet will be forwarded to the neighbour device using Layer 2 in the ARP example below. If that is not the case, does the device network card configuration include a router address through which that destination can be reached? (default gateway) Device then look

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