bash/dhcp-option.sh

   1 #!/bin/bash
   2 #Experimental BASH script to compile DHCP options
   3
   4 dec_to_hex() {
   5         echo 'obase=16; '"$1" | bc
   6 }
   7
   8 dec_to_hex_right() {
   9         echo -n $(while true; do echo -n 0; done | head -c "$2")$(dec_to_hex "$1") | tail -c "$2"
  10 }
  11
  12 escape() {
  13         #Adds \x escapes to hexdump string
  14
  15         while read -n 2 i; do
  16                 [ -n "$i" ] && echo -n '\x'"$i";
  17         done
  18 }
  19
  20 dnsmasq() {
  21         #Converts \x00\x00 notation to 00:00 notation
  22
  23         sed -e 's/^\\x//g' | sed -e 's/\\x/:/g'
  24 }
  25
  26 dhcp_option() {
  27         #Compile DHCP option using option number and data.
  28         #Generates hex string including header with option number and data length.
  29
  30         separator='\x'
  31         option_id="$1"
  32         option_data="$2"
  33
  34         len=$(echo -n "$option_data" | wc -c)
  35         dec_to_hex_right $option_id 2 | escape
  36         dec_to_hex_right $len 2 | escape
  37         printf "$option_data" | xxd -ps -c 256 | escape
  38 }
  39
  40 pd_prefix() {
  41         #Generate prefix sub-option to be included in PD option of DHCPv6
  42
  43         option_id=26
  44         lifetime_preferred='\x00\x00\x01\x2C'
  45         lifetime_valid='\x00\x00\x01\x2C'
  46
  47         prefix_length='64'
  48         #prefix = 16 octets:
  49         prefix='\x20\x01\x06\x7c\x21\x90\x1a\x01''\x00\x00\x00\x00\x00\x00\x00\x00'
  50
  51         prefix_length_hex=$(dec_to_hex $prefix_length)
  52
  53         #echo $prefix_length_hex
  54         dhcp_option $option_id "$lifetime_preferred$lifetime_valid$prefix_length_hex$prefix"
  55 }
  56
  57 pd() {
  58         #Generate data of PF option of DHCPv6
  59
  60         iaid='\x00\x00\x00\x00'
  61         t1='\x00\x00\x01\x2C'
  62         t2='\x00\x00\x01\x2C'
  63         ia_pd_opts="$(pd_prefix)"
  64         echo -n "$iaid$t1$t2$ia_pd_opts"
  65 }
  66
  67 pd_option() {
  68         #Generate PD option of DHCPv6 (including header)
  69
  70         option_id=25
  71         dhcp_option $option_id "$(pd)"
  72 }
  73
  74 pd | dnsmasq
  75 echo