Routing
Routing is the process of selecting the best path for data packets to travel across one or more networks from a source to a destination.
ISIS Authentication
1. Intro All IS-IS protocol exchanges can be authenticated to guarantee that only trusted routing devices participate in the autonomous system (AS) routing. By default, IS-IS authentication is disabled on the routing device. We have 2 ISIS Authentication options: 2. ISIS Interface Authentication 3. ISIS Level Authentication External Resources:
ISIS Attached Bit
1. Intro In Junos, the IS-IS Attached Bit (ATT-bit) is a flag automatically set by Level-1/Level-2 (L1/L2) routers in their Level-1 Link State Packets (LSPs). It signals to pure Level-1 (L1) routers in an area that the L1/L2 router is connected to another area or the backbone, allowing the L1 routers to install a default […]
ISIS L1/L2 redistribution and summarization
1. Intro We will use the following topology to see the redistribution rules in action. As a reminder, find next the default L1/L2 redistribution rules: Note: with wide-metrics-only configured, the External L1 routes become Internal L1 routes. So, Rule 3 above essentially becomes Rule 1. This use case is fully covered in the wide-metrics-only post. […]
OSPF Sham Link
1. Intro We will demonstrate the Sham Link usage with the following setup. We have CE1 and CE2 router that have a backdoor link between them. The main path between CE1 and CE2 should be via the MPLS L3VPN, so we configured a high metric between CE1 and CE2, as depicted in the next figure: […]
OSPF Cheat Sheet
OSPF – Interior Gateway Protocol (IGP) Type: Link State Algorithm: Dijkstra Metric: Interface cost is auto-derived from bandwidth unless manually configured. Cost = reference-bandwidth / bandwidth Default reference-bandwidth = 100 000 000 (100 Mbps) External Metrics: Type 1: The sum of the internal costs plus the external cost. Type 2: Only the external cost assigned […]
OSPF Virtual Link
1. Intro For backbone areas only, create a virtual link to use in place of an actual physical link. All area border routers and other routing devices on the backbone must be contiguous. If this is not possible and there is a break in OSPF connectivity, use virtual links to create connectivity to the OSPF […]
OSPF Overload
1. Intro OSPF Overload: configure the local routing device so that it appears to be overloaded. You might do this when you want the routing device to participate in OSPF routing, but do not want it to be used for transit traffic. There is no overload bit, like we have in ISIS Overload. Instead, OSPF […]
OSPF Summarization
1. Intro In the previous post we applied OSPF basic config on our test network. We had 2 areas; one of them is a Totally NSSA area. In this post will do some OSPF route summarization on the same topology, continuing from where we left off. For easy reference find the OSPF database as it […]
OSPF Basic config
1. Intro In this post we will apply OSPF basic config on our test network. We have 2 areas; one of them will be a Totally NSSA area. In the next post will do some OSPF route summarization on the same topology. 2. OSPF Basic config We will configure a topology with multiple areas: The […]
ISIS Cheat Sheet
ISIS – Interior Gateway Protocol (IGP) Type: Link State Algorithm: Dijkstra Metric: 10 for any interface0 for Loopback interface Metric Type: Narrow and Wide by default. But, ISIS silently limits metric to 63.In modern ISIS deployments we should enable wide-metric-only. Preference (AD): 15 / 18 (L1/L2 Internal)160 / 165 (L1/L2 External) PDU Types IIH IS-IS […]