## Network Layer Decodes

### Class ICMP

Provides access to fields in an (IPv4) ICMP header.

Instance Variables
type | icmp.type -> anInteger
| ICMP message type
code | icmp.code -> anInteger
| ICMP message code
checksum | icmp.checksum -> anInteger
| ICMP checksum
data | icmp.data -> aByteArray
| All the ICMP bytes, i.e. header and payload. Use this if you need to work with some of the ICMP message types that python-libtrace doesn't decode fully
payload | icmp.payload ->anIP for types 3, 4, 5, 11 and 12, otherwise aByteArray
| Most ICMP messages carry some content from the packet that triggered them; icmp.payload returns as much as it can of the triggering packet

The content of an (IPv4) ICMP header varies depending on its type field. python-libtrace decodes the following types ...

Echo Request (type 8) and Echo Reply (type 0)
ident | icmp.echo.ident -> anInteger
| Echo identifier
sequence | icmp.echo.sequence -> anInteger
| Echo sequence number

Redirect (type 5)
gateway | icmp.redirect.gateway -> anIPprefix
| Returns IPv4 address of the gateway

Nevil Brownlee
Sat, 22 Oct 16 (NZDT)