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Webcast-Catalyst9k
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Discussion on GRE Tunnel and GRE Tunnel Configuration

Can someone please point me to some good document discussing GRE Tunnel and GRE Tunnel Configuration Examples?

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2 REPLIES

Re: Discussion on GRE Tunnel and GRE Tunnel Configuration

Hi,

you can find an overview here:

Technology Support: IP Tunneling

Some documets to begin with:

GRE Overview and Troubleshooting (a very nice summary)

Implementing Tunnels (contains some GRE parts)

Why Can't I Browse the Internet when Using a GRE Tunnel (Troubleshooting)

Resolve IP Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPSEC (Troubleshooting)

HTH

Rolf

Super Bronze

Re: Discussion on GRE Tunnel and GRE Tunnel Configuration

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Posting

Rolf's references cover GRE very well.

Just wanted to emphasis, some of the "optional" settings can be advantageous.  First, I like using "keepalive 1".  This insures tunnels goes "down" if reachability is lost to other side.  This is handy even on links where you're running a dynamic routing protocol if you're also running SNMP monitoring, as the latter usually "alarms" well when an interface goes down and perhaps not so well when a routing protocol loses a neighbor.

Using mss-adjust (if supported) and the correct MTU related commands helps deal with fragmentation issues which often are adverse to performance.  Do, though, keep in mind, IP/TCP overhead can be larger than 40 bytes, so setting mss-adjust to 1436 isn't a guarantee of success even with end-to-end Ethernet supporting 1500 MTU.

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