Gre on Aaron's Worthless Words

Network Protocol Overhead

Mon, 10 Jan 2011 00:00:00 +0000

Here are some packet overhead numbers for a few popular protocols to help with doing bandwidth requirement calculations. This may be another add-as-we-go post, so please comment with additions or corrections.

Ethernet : 20 bytes
Frame Relay : 4 - 6 bytes
PPP : 6 bytes
MLPPP: 10 bytes
MPLS : 4 bytes

IP : 20 bytes

TCP : 20+ bytes
UDP : 8 bytes
GRE: 4 - 20+ bytes

Stubby Post - A Story on VPN Hardware Acceleration

Mon, 01 Nov 2010 00:00:00 +0000

We use a hosted application that requires IPSec tunnels to the provider from different properties across the country. The ones in the lower 48 perform adequately, but the new one in Alaska is absolutely horrible.

QoS Pre-classify and Class-map Order

Sat, 06 Mar 2010 00:00:00 +0000

I’m still studying for the ONT test, so I did some labs tonight. One of them was to demonstrate the qos pre-classify command for tunnel interfaces. When you have a packet sent over a GRE tunnel, the ToS field gets copied to the GRE packet, but there’s no way to see the original packet’s higher-level headers on the way out the interface. This can be a problem if your service policy needs to see protocol, port, IPs, etc. The fix for that is to enable qos pre-classify on the tunnel interface and cyrpto map; doing so will provide a copy of the original packet to the physical interface to classify the packet thoroughly.

GRE Tunnels and Encryption

Tue, 18 Mar 2008 00:00:00 +0000

GRE tunnels rock. They are interfaces on a router that are used to “connect” to another router somewhere on your LAN, your WAN, the Internet, wherever. The most popular use for them is for router-to-router VPNs.

I’ll let my friend Josh from blindhog.net show you how to do it. He’s got a video on how to configure the tunnels, and another on how to set it up for VPN.