ECP-206 Exam Dumps : Ericsson Certified Associate - IP Networking

MTU mismatch would cause an IS-IS adjacency between two routers to fail. MTU stands for maximum transmission unit, which is the maximum size of a packet that can be transmitted on a link. IS-IS hellos are padded to the full MTU size, partly to allow a router to implicitly communicate its MTU to its neighbors. If two routers have different MTUs on their interfaces, they will not be able to exchange hellos properly, and their adjacency will not form or will be dropped34. To solve this problem, the MTUs on both interfaces must be configured to match.

SEL, context, and SysID are not fields that would cause an IS-IS adjacency failure. SEL stands for selector, which is a one-octet field that identifies the network layer service to which a packet should be sent. For IS-IS routers, the SEL must always be 005. Context is not a field in IS-IS packets, but rather a term used to describe the scope of routing information in different levels or areas6. SysID stands for system identifier, which is a six-octet field that uniquely identifies a router within an area. SysID does not have to match between two routers for them to form an adjacency7.

References: MTU Mismatch Problem in IS-IS - Cisco, IS-IS adjacency is not formed due to MTU mismatch - Cisco Community, IS-IS NSAP address - Cisco Community, Understanding IS-IS Routing Contexts - Juniper Networks, IS-IS - Nokia

Referring to the exhibit, the service provider should implement L3VPN using the MP-BGP protocol to connect the sites for two customers (indicated in red and green in theexhibit). L3VPN is a type of VPN that uses MPLS to provide IP connectivity between customer sites across a service provider network. L3VPN allows customers to use overlapping or identical IP addresses without causing conflicts or requiring NAT. L3VPN uses MP-BGP to exchange VPN routes between PE routers, which are routers that connect customer networks to the service provider network. MP-BGP is an extension of BGP that can carry multiple address families, such as VPNv4 or VPNv6, along with additional attributes, such as route distinguisher (RD) and route target (RT). RD is used to make customer routes unique within the service provider network, while RT is used to control which routes are imported or exported between different VPNs3 .

References: L3VPN - Layer 3 Virtual Private Networks - Mpirical, [Use of MP-BGP Extensions for IPv6 Interdomain Routing]

Penultimate hop popping (PHP) is a function performed by certain routers in an MPLS enabled network. It refers to the process whereby the outermost label of an MPLS tagged packet is removed by a label switch router (LSR) before the packet is passed to an adjacent label edge router (LER). The purpose of PHP is to reduce the load on the LER, as it saves one cycle of label lookup. The LER can forward the packet based on its IP header or another label in the stack, without having to process the outer label. PHPfunctionality is achieved by the LER advertising a label with a value of 3 to its neighbors. This label is defined as "implicit-null" and informs the neighboring LSRs to perform PHP12.

References: Penultimate hop popping - Wikipedia, MPLS Penultimate hop popping - NetworkLessons.com