Tag: routing

Unable to access Cisco ASA through AnyConnect VPN?

I stepped on this issue few weeks ago. I was implementing a new ASA Firewall solution, first time for me with software newer than version 8.4.2

It seems that all those stories about changes in the NAT logic after that version were true. This is what I found out about ASA packet processing.firewall

Configuration was really straightforward and everything worked fine except one thing. When connected remotely using Cisco AnyConnect I was able to access all devices inside the network (inside ASA firewall), but not the ASA itself. I wasn’t able to connect with SSH nor with ASDM.

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Juniper vMX Multicast Configuration

I’m fairly new to Juniper CLI. For one of my first tries, I decided to make my life difficult by starting with multicast configuration on virtual vMX routers running as VMs on VMware ESXi.

It took a lot of investigation about some part of this configuration specially the tunnel interface which you will see below. I decided to put it here all in one place with the explanation of every step because Juniper documentation tends to assume that you know more than me. If that is not the case, this short description is for you.

Here’s how the topology looks like. I have 8 routers making this topology with the plan to source multicast streams from right to left, from PC 10.10.99.11 towards PC 10.10.98.11

Juniper vMX topology

Configuration

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VRF – Virtual Routing and Forwarding

(Part II) Virtual Routing and Forwarding

This is the second part in the series of posts dedicated to network virtualization and path isolation.

Ever needed one extra router? It’s possible to split the router into more logical routers by using VRF. How? Here’s how!

Virtual Routing and Forwarding or VRF allows a router to run more that one routing table simultaneously. When running more routing tables in the same time, they are completely independent. For example, you could use overlapping IP addresses inside more VRFs on the same router and they will function independently without conflict (You can see this kind of overlap in the example below). It is possible to use same VRF instance on more routers and connect every instance separately using VRF dedicated router port or only a sub-interface.

You can find VRFs to be used on ISP side. Provider Edge (PE) routers are usually running one VRF per customer VPN so that one router can act as a PE router for multiple Customer Edge (CE) routers even with more customers exchanging the same subnets across the VPN. By running VRF per customer, those subnets will never mix in-between them.

VRFs are used to create multiple virtual routers from one physical router.

Every VRF is creating his own Routing table and CEF table, basically a separate RIB and FIB.

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Static Route Load Balance

How it works?

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.

static route load balancing

 

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

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What is route recursion

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 looks at his local ARP table. Does it include a MAC address associated with the destination IP address?
    • If the destination is not part of the local subnet, does the local ARP table contain the MAC address of the nearest router? (MAC address to IP address mapping of default gateway router)