DynamicRouting
Contents
Subpages
/BGP /EIGRP /OSPF |
Common
Abbreviations
- ACL
- Access Control List
- AF
- Address Family
- AFI
- Address Family Identifier
- AIGP
- Accumulated Interior Gateway Protocol
- AS
- Autonomous System
- ASN
- Autonomous System Number
- BGP
- Border Gateway Protocol
- CE
- Customer Edge
- DD
- Database Description packages
- DUAL
- Diffusing Update ALgorithm
- eBGP
- External BGP
- EGP
- Exterior Gateway Protocol
- EIGRP
- Enhanced Interior Gateway Routing Protocol
- EOR
- End Of RIB
- EVPN
- Ethernet Virtual Private Network
- FIB
- Forwarding Information Base
- GR
- Graceful Restart
- HA
- High Availability
- iBGP
- Internal BGP
- IGP
- Interior Gateway Protocol
- IGRP
- Interior Gateway Routing Protocol
- IRR
- Internet Routing Registry
- IXP
- Internet Exchange Point
- L2VPN
- Layer 2 Virtual Private Network
- LIR
- Local Internet Registry
- LSA
- Link State Advertisments
- LSDB
- Link State Database
- LSR
- Link State Request
- LSU
- Link State Update
- Packet that may contain multiple LSAs
- MBGP
- Multicast BGP
- MP-BGP
- Multi-Protocol BGP
- NLRI
- Network Layer Reachability Information
- NSF
- Non Stop Forwarding
- NSR
- Non Stop Routing
- OSPF
- Open Shortest Path First
- PA
- Path Attribute
- PE
- Provider Edge
- PMTUD
- Path MTU Discovery
- RIB
- Routing Information Base
- RIR
- Regional Internet Registry
- RR
- Route Reflector
- RS
- Route-Server
- RTP
- Reliable Transport Protocol
- SAFI
- Subsequent Address Family Identifier
- SIA
- Stuck In Action
- SNM
SubNet Mask
- Tier 1 transit provider
- An IP transit provider that can reach any network on the Internet without purchasing transit services.
- SSO
- Stateful Switchover
- uRPF
- Unicast Reverse Path Forwarding
- VXLAN
- Virtual eXtensible LAN
- EoR
- End of RIB
- VTEP
- Virtual Tunnel Endpoint
- VLSM
- Variable Length Subnet Mask
EoI
Administrative distance
Wiki EN Administrative distance
Administrative distance (AD) or route preference is a number of arbitrary unit assigned to dynamic routes, static routes and directly-connected routes. The value is used in routers to rank routes from most preferred (low AD value) to least preferred (high AD value). When multiple paths to the same destination are available in its routing table, the router uses the route with the lowest administrative distance.FRR Docs - Zebra #Administrative distance
Administrative distance allows FRR to make decisions about what routes should be installed in the rib based upon the originating protocol. The lowest Admin Distance is the route selected.
Autonomous system (AS)
IETF RFC1930 - Guidelines for creation, selection, and registration of an Autonomous System (AS)<<BR>
- Autonomous System (AS)
- An autonomous system (AS) is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators on behalf of a single administrative entity or domain, that presents a common and clearly defined routing policy to the Internet.
- Each AS is assigned an autonomous system number (ASN),
for use in Border Gateway Protocol (BGP) routing.
- Autonomous System Numbers are assigned to Local Internet Registries (LIRs) and end-user organizations by their respective Regional Internet Registries (RIRs), which in turn receive blocks of ASNs for reassignment from the Internet Assigned Numbers Authority (IANA).
- The IANA also maintains a registry of ASNs which are reserved for private use (and should therefore not be announced to the global Internet).
Autonomous system numbers (AS)
- 16 bit
- Completely allocated
Number
Description
Reference
Registration Date
0
Reserved
64496-64511
Reserved for use in documentation and sample code
[RFC5398]
2008-12-03
64512-65534
Reserved for Private Use
[RFC6996]
65535
Reserved
[RFC7300]
- Completely allocated
- 32 bit
- 16 bit ASNs are contained
- Lots of free unallocated address space
Number
Description
Reference
Registration Date
65536-65551
Reserved for use in documentation and sample code
[RFC5398]
2008-12-03
65552-131071
Reserved
4200000000-4294967294
Reserved for Private Use
[RFC6996]
4294967295
Reserved
[RFC7300]
Router ID
Looks like an IP address, but is just a name.
- Router ID should be configured.
- Can be configured for multiple routing protocols differently.
- If there is no configured router-ID, the highest IP address on a loopback-address is assigned as the Router ID
- If there is no loopback-interface, the highest IP address on an interface is assigned as the Router ID.
- If addresses cannot be determined (e.g. if FRR has noc connection to zebra)
the router id is set to 0.0.0.0
Number of adjacencies in a full mesh
A = n * (n -1) / 2
Wildcard mask
WILDCARD_MASK = 255.255.255.255 - SUBNET_MASK
Network command
- Defines just address space not network to be advertised
- If an interface address falls into this address space, the network belonging to the interface is advertised
- In IPv6 interface commands are used.
EoI
Advanced routing
Route aggregation
- Reduces the size of the routing table
- Makes routing tables more readable
- Increases the efficiency routing table
- Saves cycles and memory
- Works best if summarization is already considered when assigning subnet addressing
- Plan your networks
- Algorithm
- Binary AND of network prefixes to determine common bits.
- Appending bits with value 0 of the resulting network address are counted, subtracted from the maximum length of the SNM (32/128) and converted to decimal to calculate the subnet mask.
- Summarized network address and SNM are concatenated to the summarized network prefix.
- Summarized address
- Be careful, because summarization may also span holes, which may cause issues.
- Should work, because advertisements of network falling into that route are more specific.
- Network with the least cost (OSPF) or highest metric (EIGRP) is picked for the summarized route.
Determine if automatic summarization is configured Automatic summarization
1 show ip protocols
EoI
Route redistribution
- Use cases
- If there is more than one IGPs or IGP instances
- e.g. after a merge of companies
- different departments under different administrative control
- Connection to partner networks
- IPG routes need to be advertised into BGP
- BPG routes need to be advertised into IGP
- If there is more than one IGPs or IGP instances
- Seed/Default metric
- Metrics are very different between RPs and but need to be meaning full
- assigned, by default, to redistributed routes, when no metric is manually configured, if a route is imported into a routing protocol
Target Routing Protocol
Default Seed Metric
RIP
infinity
EIGRP
infinity
OSPF
20 (1 for BGP)
BGP
Uses IGP metric value
in multi-exit descriminator (MED)
redistribute command and default metrics
Meaning of the command:
- "Redistribute routes from a specified routing source into this routing protocol."
- Options:
- Set a default metric for all routing protocols being injected into a specific routing protocol.
Set a metric as part of the redistribute command.
- Set a matrix via route-map
Redistribute into OSPF process 1
(updates the area using OSPF external type 2 LSAs)
Redistribute into OSPF process 1
(updates the area using OSPF external type 1 LSAs)
Set the metric-type to 1 changes the metric calculation. With type 2 the cost value was constant throughout the entire area. With type 1 the cost of the path is added (to the default metric), which is much more accurate in larger topologies.
Redistribute into EIGRP ASN 1
(routes will not be injected into rib because the default metric is infinity)
Assign default-metric in eigrp for all routing protocols
1 conf term
2 router eigrp 1
3 ! Bandwidth BW … uINT32 [kbps]
4 ! Delay D … uINT32 [units of 10 µs]
5 ! Reliability R … BYTE ([low] 0-255 [high])
6 ! Load L … BYTE ([low] 0-255 [high])
7 ! Maximum Transmission Unit MTU … uINT16 (1-65535)
8 ! default-metric BW D R L MTU
9 default-metric 1000000 1 255 1 1500
Assign default-metric in ospf
Assign default-metric in eigrp
1 conf term
2 router eigrp 1
3 ! DEFAULT METRIC MAY BE REMOVED BEFOREHAND
4 ! no default-metric
5 ! REMOVE OLD REDISTRIBUTION COMMAND
6 ! no redistribute ospf 1
7 ! Bandwidth BW … uINT32 [kbps]
8 ! Delay D … uINT32 [units of 10 µs]
9 ! Reliability R … BYTE ([low] 0-255 [high])
10 ! Load L … BYTE ([low] 0-255 [high])
11 ! Maximum Transmission Unit MTU … uINT16 (1-65535)
12 ! redistribute ospf 1 metric BW D R L MTU
13 redistribute ospf 1 metric 1000000 1 255 1 1500
Assign default-metric in eigrp using a route-map
Redistribution Loops
Issue:
- Area/AS A publishes a route to another Area/AS B.
- Area/AS Bs secondary router publishes the route back to Area/AS A with a lower metric.
- A sub-optimal path is selected.
Solutions:
- Higher-Metric of redistributed routes
- Adjust Administrative distance
- eBGP is more believable than EIGRP
- OSPF is more believable than RIP
- Filter routes (e.g. on ABR, ASBR or during injection to the RIB)
- Tag the routes
Set tag on redistribution (from Area/AS A to Area/AS
- Deny tag on redistribution (from Area/AS B to Area/AS A)
IP SLA
Use cases
- Measure network performance (like jitter)
- RTR Response Time Reporter/RealTime Responder
- Influence routing decisions
Response Time Reporter (RTR)
- Configure a router to be a RTR
- Configure a router to be a RTR
Track IP SLA operation to switch static routes
1 conf term 2 ! DEFINE OPERATION ENTRY 3 ip sla 1 4 ! PING INGRESS IFACE ON TARGET ROUTER 5 icmp-echo IP-ADDRESS_NEXTHOP1 source-ip SRC-IP 6 frequency 30 7 ! 100ms THRESHOLD 8 threshold 100 9 exit 10 ! SCHEDULE OPERATION ENTRY 11 ip sla schedule 1 life forever start-time now 12 ! CREATE A TRACKER THAT FOLLOWS OPERATION 1 13 track 1 ip sla 1 14 ! COUNTER ROUTE FLAPPING (HYSTERIS) 15 delay down 10 up 10 16 exit 17 ! CREATE A ROUTE THAT IS TRIGGERED ON TRACKER 1 18 ip route PREFIX SNM NEXT-HOP1 track 1 19 ! CREATE A ROUTE WHOSE ADMINISTRATIVE DISTANCE 20 ! (LAST POS ARG, DEFAULT FOR STATIC ROUTES 1) 21 ! IS HIGHER (LESS PREFERABLE) THAN THE PREVIOUS ROUTE 22 ip route PREFIX SNM NEXT-HOP2 2 23 ! CHECK WITH 24 show track 1
Policy-based routing (PBR)
- Routing decisions based on a policy
Configure an alternative route only for a single host