DHCP Relay TR-101 Support Introduction
7-11
Software Reference for SwitchBlade x3100 Series Switches (Network Management)
When DHCP Relay is enabled (in either Relay or Snooping mode) for a given customer interface, it can be con-
figured to automatically age the allocated IP address and then to automatically remove the IP address from the
DHCP Relay tables. This makes room for another entry in its tables. When DHCP Relay has been configured
and auto-age enabled (
AGEING=ON), then DHCP Relay will automatically remove the IP address when the IP
address ages out. The ageing will be based upon the lease-time specified in the DHCP ACK packet that is
received from the DHCP server.
The Auto-Ageing feature will save the lease time and the DHCP server's IP (“server identifier” option field)
address upon receiving a DHCP ACK packet. If the DHCP ACK packet has a lease time of 0, there is no ageing
(infinite), and this will replace any previous lease value.
The DHCP Relay entry and the IP filter will be removed when one of the following occurs:
• Lease time expires (unless the lease is infinite)
• Receive a DHCP NAK from the DHCP server that the current IP address was allocated
• Receive a DHCP Decline packet from the DHCP client with the ciaddr of the currently allocated IP address
• Receive a DHCP Release packet from the DHCP client with the ciaddr of the currently allocated IP address
(this would occur if the client moved to another port).
7.2.6 DHCP Relay TR-101 Support
The capabilities for TR-101 are described in the DSL Forum Technical Report for TR-101 (http://www.dslfo-
rum.org/techwork/tr/TR-101.pdf).
TR-101 information is contained in sub-options 1 and 2 in the DHCP Relay Agent option (option 82). The for-
mat of option 82 is defined in IETF RFC 3046. Sub-option 1 contains the agent circuit ID. Sub-option 2 contains
up to 63 characters of text information for the agent remote ID.
7.2.6.1 Current TR-101 Format
The TR-101 format is text rather than binary, with the basic structure as follows:
If the shelf-id is less than 30 characters long, it is padded with characters at end of the string to force it to 30
characters. The slot, port, subif, and vid are prepended with zeros to force them to the desired length.
TABLE 7-1 Sub-option 1 for TR-101 (Text)
Characters30 13 12 131314
Attribute Shelf-ID Ethernet
Address
(MAC)
Slot / Port / Sub-
inter-
face
VID
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