Header on Aaron's Worthless Words

Frame Relay Notes - LMI, Headers, and Encapsulation

Thu, 23 Jun 2011 00:00:00 +0000

Local Management Interface

Manages link between the router and frame relay switch
Routers send Status Enquiry to the switch
The switch responds with a Status message informing the router of the DLCIs available
Serves as a keepalive
Default keepalive is 10 seconds, 3 misses is failed
Three types
- cisco <- default
- ansi (Annex D)
- q933a

R1(config)#interface s1/0
R1(config-if)#frame-relay lmi-type ansi

Headers and Encapsulation

Link Access Procedure for Frame-mode Bearer Services (LAPF) is the first header
- Includes DLCI, DE, FECN, BECN
- To be read by the frame relay switch
Frame relay encapsulation header is next
- To be read by the router on the other end of the VC
Two types
- cisco : proprietary <- default
- ietf : IETF RFC 2427

R1(config)#interface s1/0
R1(config-if)#frame-relay encapsulation ietf <- for all DLCIs
- or -
R1(config-if)#frame-relay interface-dlci 100 ietf <- for specific DLCIs
- or - 
R1(config-if)#frame-relay map ip 10.0.0.1 ietf <- for specific DLCis

Wireshark and EtherIP Packets

Sat, 04 Jun 2011 00:00:00 +0000

I got a call from our Systems and Security guys today to talk about a Wireshark capture they had done from a user VLAN. They had noticed two frames that were destined for some seemingly random host in the same network as they were in, but the source and destination IP addresses reported by Wireshark made no sense. The frames were from a web server to an IP address on our wireless network. The web server is on the other side of the firewall, and the wireless network is on the other side of the controller; there was no reason at all that a packet with that source and destination would show up here.

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