3-4 - PE-to-CE Routing Requirements in Layer 3 MPLS VPNs Flashcards
What are the 3 main goals of L3VPN design?
- The MPLS VPN backbone should look like a standard corporate backbone to the CE routers.
- The provider core or backbone routers (P) are hidden from the customer.
- The CE routers run standard IP routing software and exchange routing updates with the PE routers.
What are the options for PE-CE protocols?
- EIGRP
- RIPv2
- OSPF
- eBGP
- Static Routes
T/F: The PE routers are the only routers in MPLS VPN architecture that see all routing aspects of the MPLS VPN.
True
What route exchange actions do the PE routers perform?
- PE routers exchange IPv4 VPN routes with CE routers through various routing protocols that run in the virtual routing tables
- PE routers exchange VPNv4 routes through MP-IBGP sessions with other PE routers
- PE routers exchange core routes wtih provider core routers and other PE routers through a core IGP
Describe the following configuration.
IOS-XR Command:
router static
vrf
address-family ipv4 unicast
[x.x.x.x/xx] [x.x.x.x]
- enters the router static, vrf, address-family ipv4 subconfig mode and adds a route with a network address, CIDR, and next-hop
Describe the following configuration.
IOS/IOS-XE Command:
ip route vrf [network address] [subnet mask] [next-hop IP]
from global config mode, adds a VRF-specific static route to a particular network and specifies the next-hop
Describe the following configuration.
IOS-XR Command:
router eigrp 1
vrf Customer_A
address-family ipv4
default-metric 10000 100 255 1 1500
autonomous-system 1
redistribute bgp 64500
interface GigabitEthernet0/0/0/0
!
router bgp 64500
vrf Customer_A
rd 64500:1
address-famiy ipv4 unicast
redistribute eigrp 1
this configuration configures a VRF specific instance of EIGRP and redistributes that into BGP. Additionally, BGP routes are redistributed into EIGRP.
Describe the following configuration.
IOS/IOS-XE Command:
router eigrp 1
address-family ipv4 vrf Customer_A autonomous-system 1
network 10.0.0.0 255.255.255.0
redistribute bgp 64500 metric 10000 100 255 1 1500
no auto-summary
!
router bgp 64500
address-family ipv4 vrf Customer_A
redistribute eigrp 1
no auto-summary
EIGRP routes are converted to iBGP routes and transported through the BGP core network.
T/F: BGP extended communities carry and preserve EIGRP metrics when they cross the MP-IBGP domain.
True
What BGP attribute does the IGP metric get copied into on L3VPNs?
multi-exit discriminator (MED)
Describe the OSPF “superbackbone” in L3VPN environments.
- implemented with MP-BGP between the PE routers but is otherwise transparent to the OSPF routers
- allows disjointed OSPF backbone areas (area 0) at MPLS VPN customer sites
GOALS:
superbackbone will not use standard OSPF-BGP redistribution
OSPF continuity must be provided between OSPF sites
Internal OSPF routes remain internal OSPF routes
External OSPF routes remain external OSPF routes
Non-OSPF routes that are redistributed into OSPF must appear as external OSPF routes in OSPF
OSPF metrics and metric types (E1 and E2) must be preserved
OSPF superbackbone will be transparent to the CE routers that run OSPF software
T/F: A BGP extended community is defined to carry the OSPF route type and OSPF area across the BGP backbone. The OSPF cost is carried in the MED attribute.
True
The PE routers that connect regular OSPF areas to the superbackbone appear are not considered ABRs in the OSPF areas to which they are attached.
False. They are considered ABRs in the OSPF areas to which they are attached. ABRs also appear as ASBRs in nonstub areas.
T/F: A BGP extended community is defined to carry the OSPF route type and OSPF area across the BGP backbone. The OSPF cost is carried in the MED attribute.
True
Describe the following configuration.
IOS/IOS-XE Commands:
router ospf 10 vrf Customer_A
redistribute bgp 64500 subnets
network 192.168.1.1 0.0.0.0 area 0
!
router bgp 64500
address-family ipv4 vrf Customer_A
redistribute ospf 10
exit-address-family
Configures OSPF and BGP, and redistributes learned routes between both protocols.
