Dhcp - Recover Lost Ip Address (Link-Local Ip); Table 25: Diag. - Calculating Local Link Ip Addresses; Fig. 70: Diag. - Dhcp Discovery Timing Diagram - Redline RDL-3000 Series User Manual

RDL-3000 FAMILY
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.
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!
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:
Order
Seg
1st
F7
Seg
2nd
F7
Seg
3rd
(F7
70-00158-03-00

Fig. 70: Diag. - DHCP Discovery Timing Diagram

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

Table 25: Diag. - Calculating Local Link IP Addresses

Segment / Calculation
5
= 247
16
5 3
Seg
XOR
02 = F5 = 245
XOR
16 16 16
5 3 1
XOR Seg XOR Seg
02 00 =F5
)
XOR XOR
16 16 16
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USER MANUAL
Segment /Calculation
6
Seg
1A = 26
16
6 4
Seg Seg
XOR
1A 13 = 9
XOR
16 16
6
Seg XOR Seg
= 245 (1A 13 )
XOR
16 16 16
IP Address
169.254.247.26
169.254.245.9
= 9
16
4 2
XOR Seg
169.254.245.0
09 = 0
XOR
16 16
Page 153 of 254 April 17, 2015