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Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
Chapter 7 Configuring IP Unnumbered on IEEE 802.1Q VLANs
Feature History for IP Unnumbered on VLANs
When a subinterface goes down, the IP host route exists until the DHCP lease time expires. However, if
you enter the show ip route dhcp command, the IP host routes do not display. After the subinterface
comes back up, the IP host routes display when you enter the show ip route dhcp command if the DHCP
lease time has not expired.
This chapter describes the IP Unnumbered on IEEE 802.1Q VLANs feature in the following topics:
• Feature History for IP Unnumbered on VLANs, page 7-2
• Benefits for IP Unnumbered on VLANs, page 7-2
• Restrictions for IP Unnumbered on VLANs, page 7-3
• Configuration Tasks for IP Unnumbered on VLANs, page 7-3
• Configuration Examples for IP Unnumbered on VLANs, page 7-4
• Monitoring and Maintaining IP Unnumbered Ethernet VLAN Subinterfaces, page 7-5
Feature History for IP Unnumbered on VLANs
Benefits for IP Unnumbered on VLANs
The IP Unnumbered on VLANs feature benefits service providers in the following ways:
• DSL providers can easily migrate their ATM networks to IP networks and migrate their DSLAMs
from an ATM uplink to a Gigabit Ethernet uplink for connection to the router.
• Using one router and the same service model, providers can aggregate Layer 2 access for DSL and
Metro-Ethernet subscribers.
• IP address space is saved because all ports can share the same subnet.
• Each IP unnumbered subinterface supports one VLAN and each VLAN can have multiple IP
addresses.
• Subscribers are easily identified, which makes it possible to apply different policies on a
per-subscriber basis.
• DHCP simplifies address management.
• The use of VLANs increases security.
• Security is greater with the use of VLANs. Because routing information is obtained from DHCP,
ARP and MAC entries cannot be spoofed.
Cisco IOS Release Description Required PRE
12.3(7)XI1 This feature was introduced on the Cisco 10000 series
router.
PRE2
12.2(28)SB This feature was integrated into Cisco IOS Release
12.2(28)SB.
PRE2