Information Technology Reference
In-Depth Information
When ASBR3 receives the packet, it has two labels. The top label (19) is the BGP label L6,
and the bottom label (22) is the VPN label Lv. The top label 19 is then replaced by another
BGP label (19). Because of PHP, ASBR3 does not push an IGP label. Label swapping con-
tinues until PE1 receives the packet with Lv, and then an IP packet is delivered to the CE.
Comparison of Various Inter-AS VPN Options
So far, four inter-AS VPN options have been presented. Table 10-7 compares and contrasts
them.
Table 10-7
Comparison and Contrast of Four Inter-AS Options
Inter-AS
Label
Inter-AS
Filtering
Option
Complexity
Scalability
Back-to-back
VRF
Standard IPv4
without labels
PEs need to filter
IPv4 routes from the
remote AS per VRF.
Low
Configurations are
similar to the basic
(same AS) VPN.
Low
One VRF/interface is
required per ASBR CE.
ASBR PEs hold all (IPv4
and VPNv4) routing
information.
Single-hop
eBGP for
VPNv4
VPNv4 labels
RTs should be
filtered from the
remote AS.
ARF is disabled.
Medium
VPNv4 labels are reset at
ASBRs.
BGP next hop can be
made reachable at the
receiving AS by redistri-
bution or
next-hop-self
.
Medium
Only one interface is
required between ASBRs.
No VRFs are required on
ASBRs.
ASBRs hold VPNv4
information for their own
AS and might hold the
VPNv4 information for
the remote AS, depending
on the next-hop
configuration.
Multihop
eBGP for
VPNv4
IPv4 labels
IPv4 addresses and
labels should be
filtered for inbound
and outbound.
High
VPNv4 information is
exchanged between
RRs with the next hop
unchanged.
IPv4 with labels are
exchanged on the inter-
AS links.
High
VPNv4 routes are
exchanged between RRs.
ASBRs are not involved
in VPNv4 information
exchange.
