RDL-3000
FAMILY
USER MANUAL
70-00158-03-00
Proprietary Redline Communications © 2015
Page
153
of 254
April 17, 2015
5.5.2
DHCP - Recover Lost IP Address (Link-Local IP)
When DHCP is enabled, a DHCP server is contacted to configure the IP address, subnet
mask, and default gateway address. At reboot, the system has no IP address until the
server is contacted using DHCP discovery. The subscriber IP address is disabled
immediately when the link to the sector controller is lost.
When a link is established, the subscriber performs a DHCP discovery by broadcasting a
series of requests to contact a DHCP server. The RDL-3000 has no addressable IP
while the DHCP discovery process is active. The aggregate timeout for the request
sequence is approximately 520 seconds. If DHCP discovery can not contact a DHCP
server within the timeout period, the local link IP is activated for 300 seconds. This
period allows an operator to login and change system settings. At the end of 300
seconds, the IP address is disabled and the discovery function is restarted. This cycle
repeats until a DHCP discovery is successful.
Fig. 70: Diag. - DHCP Discovery Timing Diagram
The default IP subnet mask is: 255.255.0.0 and one of three default IP addresses are
assigned to the subscriber. The default addresses are generated as the default prefix
'169.254' plus two values generated from the unit MAC address. With DHCP disabled,
the operator may use the CLI command 'dhcp on' to display the three link local IP
addresses for that unit. For example:
10.101.30.1(set)# dhcp on
-- Notice: Need to run 'apply config' or 'save config' to take effect!
If DHCP server not found after 4 retries, the system will
select one of the Link Local addresses:
169.254.247.26, 169.254.247.9, and 169.254.245.0
The first address is generated using the fifth and sixth segments in the MAC address. If
the first Link local IP address is in-use, a second address is generated using an XOR of
the original results with the third and fourth segments in the MAC address. If required, a
third address is generated using the second results and the first and second segments.
For example, if the remote unit MAC address was 00-09-02-13-F7-1A:
Table 25
:
Diag. - Calculating Local Link IP Addresses
Order
Segment / Calculation
Segment /Calculation
IP Address
1st
Seg
5
F7
16
= 247
Seg
6
1A
16
= 26
169.254.247.26
2nd
Seg
5
XOR
Seg
3
F7
16
XOR
02
16
= F5
16
= 245
Seg
6
XOR
Seg
4
1A
16
XOR
13
16
= 9
16
= 9
169.254.245.9
3rd
Seg
5
XOR Seg
3
XOR Seg
1
(F7
16
XOR
02
16
)
XOR
00
16
=F5
16
= 245
Seg
6
XOR Seg
4
XOR Seg
2
(1A
16
XOR
13
16
)
XOR
09
16
= 0
16
169.254.245.0
