EIGRP

1. Enchanced interior gateway routing protocol
   1. Named mode
   2. Metric
   3. Timers
   4. Neighbourship
   5. RID
   6. Messages
   7. EIGRP header
      1. IP internal route TLV
      2. IP external route TLV
      3. Multiprotocol TLV
   8. CLI
      1. IOS XE
      2. NX-OS
2. Point-to-multipoint setup
3. Diffusing update algorithm (DUAL)
   1. Stuck in active (SIA)
4. Convergence
   1. Successor and feasible successor
   2. Stub
   3. Summary
   4. Loop-free alternative (LFA)
5. Authentication
6. RIB scale
7. Redistribute
8. IPv6
9. Graceful restart
10. MPLS
    1. Cost-community
    2. Site of Origin (SoO)
11. AddPath
12. Over-the-top (OTP)
13. Conditional receive
14. ACL
15. Maximum prefix

Enchanced interior gateway routing protocol

• IP 88, CS6
• 224.0.0.10, 0100.5e00.000a
• ff02::a, 3333.0000.000a
• reliable transport protocol (RTP):
  • not TCP, because operates over mcast
• by default split horizon & poison reverse are enabled everywhere
• 500 routers per AS – limitation based on DUAL (Query flood)
• AD
  • internal: 90
  • external: 170
  • if changed, neighbourship is reset
• 32bit metric
• if routes have same metric, traffic-share has no effect
• auto-redistribute between EIGRP and IGRP within same AS
• several processes with the same AD receive same prefix (bad design):
  1. lowest metric
  2. lowest AS
• refreshes RIB timers on prefix update in topology table (not only on change!)

Named mode

• 64bit metric
• RIB scale: 64bit metric → 32bit metric (metric unit in RIB)
• if 64bit metric (named mode) cannot be scaled down to 32bit (numbered mode)
  • Query with new metric is sent ⇒ neigbour learns new metric
  • prefix is not included into Update towards neighbour with numbered mode
  • prefix is not installed in RIB

; assigns tag to internal self-originated prefixes
(config-router-af)# eigrp default-route-tag <N>

; lists IPv4 and IPv6 AF for named mode, no passive interfaces shown
# show eigrp protocols

Metric

• change of bandwidth, delay – trigger Update
• change of reliability, load, MTU – no Update triggered irrespective to K-values; values – snapshots at prefix creation
• delay = 0xffffffff ≡ infinity
• prefix metric is modified on ingress
• wide metric:
  • 256 multiplier → 65536 multiplier
  • delay – picoseconds
    1. BW ≤ 1Gbps or manual BW/delay: usual calculation
    2. BW > 1Gbps and no manual config: 10¹³/(interface BW in kbps)

(config-router)# default-metric <M1> <M2> <M3> <M4> <M5>

; tunes delay to match METRIC (256 ≡ +10µs)
(config-router)# offset-list <ACL> in|out <METRIC> [<INTF>]

Timers

1. hello
   • Hello frequency
   • local value is used
   • 5s by default (including P2P FR)
     • 60s: BW < T1, e.g., FR P2M, ATM
2. hold
   • how long to wait for reply from neighbour
   • value, supplied by neighbour, is used
   • 3 times longer than hello by default
   • not adjusted to hello automatically
3. SRTT
   • smooth round-trip timer
   • used to calculate RTO and multicast flow timer
   • time to send-receive reliable packet
4. multicast flow timer
   • how long to wait for reply to multicast message
   • if no reply received, unicast message is sent
5. RTO
   • retransmission timeout, ∈ [0.2s; 5s]
   • unicast message timeout
   • 16 sequential timeouts → tear neighbourship if hold timer expired (hold timer is active ≡ it is refreshed by Hello)
   • if hold > 80s (5s × 16), retransmit may be larger than 16
6. Active
   • SIA timeout
   • 3 mins by default

(config-if)# ip hello-interval eigrp <ASN> <sec>
(config-if)# ip hold-time eigrp <ASN> <sec>

Neighbourship

• interface addresses are in the same subnet; subnets may differ, e.g., 10.0.0.1/24 and 10.0.0.2/30
• match: ASN, K-values
• not required to match: timers, MTU
• not required to be different: RID (bad design, may lead to prefix being ignored)
• if unicast neighbourship is enabled, only Hello from configured neighbours are accepted
• between primary addresses
  • Hello is accepted on secondary address
  • secondary ≡ connected, falls under split-horizon, participates in IGP

; distinguish unicast and mcast neighbours
# show ip eigrp neighbor [detail]

RID

• selection
  1. manual
  2. loopback:
     • IOS: largest address from up/up loopback
     • NX-OS: loopback0
  3. largest address from non-loopback not in admin-down (down/down – valid!)
• must be different for
  • external routes: routes with RID, equal to local value, are ignored
  • internal routes: starting from IOS 15.0 RID is included as well – external route behaviour
• NX-OS: if blank loopback0 is assigned address – reset EIGRP process to get RID from loopback0

Messages

1. Hello
   • mcast
   • find new neighbours, keepalive to existing ones
   • receiving any EIGRP packet ≡ receiving Hello
2. Update
   • uses RTP
   • contents: prefix { prefix length, BW, delay, reliability, load, MTU, hop count }
   • mcast
     • unicast: on NBMA and P2P, on synchronization, on retransmit
   • subject to split-horizon and poison reverse: metric = infinity (0xff..ff)
3. Query
   • uses RTP
   • mcast
     • unicast: on P2P, on retransmit
4. Reply
   • uses RTP
   • unicast only
5. Ack
   • confirm Update, Query, Reply
   • Hello with RTP contents
   • unicast only
   • alternatives
     1. Update with poison reverse on prefix
     2. any reliable unicast packet: contains ack number

EIGRP header

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Version (2)  |     Opcode    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Flags                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Sequence                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              Ack                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              ASN                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                              TLV                              /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Opcode

• 1: Update
• 3: Query
• 4: Reply
• 5: Hello
• 10: SIA-Query
• 11: SIA-Reply

Ack:

• 0x00000000: mcast, ≡ Hello packet
• non-zero: unicast, acknowledge packet – last heard sequence (not next expected as in TCP)

Flags:

• 0x01: init
  • set in the first Update
• 0x02: CR-mode
  • conditional receive
• 0x04: restart (NSF)
  • signals the beginning of restart
• 0x08: end-of-table
  • signals that the whole RIB has been sent ≡ end of NSF restart ⇒ stale routes can be removed from RIB

TLV types:

• general
  • 0x0001: EIGRP parameters
    • K-values, holdtime
    • if all parameters are 0xFF ≡ peer-termination
  • 0x0002: Authentication type
  • 0x0003: Sequence
  • 0x0004: Software version
  • 0x0005: Next Multicast Sequence
• IP specific
  • 0x0102: IPv4 internal route
  • 0x0103: IPv4 external route
  • 0x0402: IPv6 internal route
  • 0x0403: IPv6 external route
• Nultiprotocol
  • 0x0602: AFI internal route
  • 0x0603: AFI external route

IP internal route TLV

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            0x0102             |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Next hop                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Delay                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Bandwidth                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  MTU                          |   Hop count   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Reliability  |      Load     | Internal tag  |     Flags     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix length |           Destination (zero-padded)           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Hop count: 0 for directly connected

Destination: significant MSB part of prefix (10.1 for 10.1.0.0/16), variable length

Flags (0x00 in practice):

• 0x01: source withdraw
• 0x02: candidate default
• 0x04: active state
• 0x08: route is replicated from another VRF

IP external route TLV

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            0x0103             |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Next hop                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Originating router RID                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Originating ASN                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Administrative tag                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   External protocol metric                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Reserved            |  Ext Proto ID |     Flags     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Delay                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Bandwidth                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  MTU                          |   Hop count   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Reliability  |      Load     | Internal tag  |     Flags     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix length |           Destination (zero-padded)           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

External protocol ID:

• 1: IGRP
• 2: EIGRP
• 3: static
• 4: RIP
• 6: OSPF
• 7: IS-IS
• 8: EGP
• 9: BGP
• 10: IDRP
• 11: connected

Multiprotocol TLV

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Type              |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Topology ID           |               AFI             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Originating router RID                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Offset    |    Priority   |  Reliability  |      Load     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  MTU                          |   Hop count   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
+             Delay             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
|                               |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+           Bandwidth           +
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Reserved            |              Flags            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+ <-- extended attributes insertion
|                           Next hop                            |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|                         External RID                          |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|                         External ASN                          |   \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    > for external
|                      Administrative tag                       |   /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|                   External protocol metric                    |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|           Reserved            |  Ext Proto ID |     Flags     |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+
| Prefix length |           Destination (zero-padded)           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

AFI:

• 1: IPv4
• 2: IPv6

Offset: 16bit units, extended attributes (TLV) size after metrics

• 0: NoOp
• 1: scaled metric
• 2: administrator tag
• 3: community list
• 4: jitter
• 5: quiescent energy
• 6: energy
• 7: AddPath

CLI

IOS XE

; mark network as candidate default, not used by this router, CLASSFUL must be in RIB
(config)# ip default-network <CLASSFUL>

; disables sending and receiving Hello, does not announce prefix by itself (network cmd required)
(config-router)# passive-interface <INTF>|default

; disables mcast Hello for the interface, unicast neighbours only
(config-router)# neighbor <IP> <INTF>

; applied to all interfaces by default
; if global and interface ACLs are defined, their intersection takes effect
(config-router)# distribute-list <ACL> [out <INTF>] [in <INTF>]

; sets AD for routes from neighbours, who match IP + wildcard; internal prefix only
(config-router)# distance <AD <IP> <WILDCARD> [<ACL>]

; enabled by default, include metric in balancing decision
(config-router)# traffic-share balanced

; send traffic towards lowest metric, other routes are on standby in RIB
(config-router)# traffic-share min

; ECMP
(config-router)# traffic-share min across-interfaces

; 500 default, for show ip eigrp events
(config-router)# eigrp event-log-size <N>

(config-router)# bfd all-interfaces|interface <INTF>

; EIGRP packet statistics
# show ip eigrp traffic

; hidden
# show ip eigrp events

; does not show passive interfaces
# show ip eigrp interface

NX-OS

(config)# feature eigrp

(config-if)# ip router eigrp <ASN>

Point-to-multipoint setup

; EIGRP traffic share, 50% by default
; logical and physical interfaces
; calculated using logical speed → may be higher than 100%
(config-if)# ip bandwidth-percent eigrp <ASN> <PERCENT>

Diffusing update algorithm (DUAL)

• process
  1. state → active
     • successor and feasible successor are lost
     • AD from both successor and feasible successor are larger than current FD
     • received Query from successor with no feasible successor available
  2. send Query to all neighbours except for old successor and feasible successor, not subject to split horizon
  3. neighbour’s prefix state equals to
     • passive:
       • send Reply that route is loop-free (≡ passive)
       • do not spread Query further
     • active
       • send out Query to neighbours
       • do not send own Reply unless own Query is replied to by everyone
       • Query for prefix counts as Reply (no prefix available); Reply to this Query is sent immediately with Infinity metric (since there is no P → A state transition)
     • does not exist
       • send Reply with Infinity
  4. all Reply received ≡ routes are loop-free, best route can be safely selected
• during DUAL prefix is frozen in RIB (counterpart of RIP holddown)

(config-router)# timers active-time <mins>|disabled

Stuck in active (SIA)

• prefix state, if not all Reply are received during Active timer
• IOS version
  • < 12.2: tear down neighbourship with routers that did not respond
  • ≥ 12.2
    • SIA process
      1. send SIA-Query at half of Active timer
         • if SIA-Reply is received, reset Active timer
      2. send up to 3 SIA-Query
         • SIA-Reply to the last SIA-Query does not reset Active timer
      3. total wait time: 360s default (90 + 90 + 90 + 90)
    • SIA-Query and SIA-Reply use RTP

Convergence

• 100ms for 1000 prefixes, 1.2s for 10k prefixes
• acceleration:
  • feasible successor
  • stub
• every hop along Query path adds ≈200ms to convergence time

Successor and feasible successor

; successor and feasible successor, all-links ≡ show all paths
# show ip eigrp topology [all-links]

; show reason for Query
# show ip eigrp topology active

Stub

• does not announce prefixes, received via EIGRP
• neighbours do not send Query to stubs
• prevents traffic transit through branch
• marker – stub bit in Hello
• options:
  1. connected
     • default
     • announce connected prefixes, if they are enabled by network command
  2. summary
     • default
     • announce manual and auto summaries
  3. static
     • announce static routes, if they are redistributed
  4. leak-map
     • announce more specific prefixes, falling under summary
     • announce matching EIGRP prefixes further via EIGRP
  5. redistributed
  6. receive-only

; connected and summary by default
(config-router)# eigrp stub

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            0x0006             |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Options             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Options:

• 0x0001: connected
• 0x0002: static
• 0x0004: summary
• 0x0008: redistribute
• 0x0010: leak-map
• 0x0020: receive-only

Summary

• AD = 5 by default – prevent routing loops
• if Query received, Reply is sent immediately, Query is not forwarded further
  • if ingress Query prefix falls under announced egress summary prefix
  • if Query prefix has no exact match in topology table (summary is not exact)
• internal route; if external prefix matches summary – announce external
• metric: best metric out of sub-prefixes, not best components
• next-hop = Null0 (including auto-summary)

; default, starting from IOS 15.0
; does not summarize external routes (but removes them from Update if fall under internal summary)
(config-router)# no auto-summary

; causes neighbourship reset or resync
(config-if)# ip summary-address eigrp <ASN> <PREFIX>

Loop-free alternative (LFA)

• extra conditions for feasible successor
• installs 1 backup path in RIB and FIB
• per-prefix
• named mode only
• tie-breakers: the lower the priority, the better
  1. SRLG: 10 default
  2. intf-disjoint:
     • 20 default
     • backup route cannot egress via the same interface, as primary
  3. lowest metric: 30 default
  4. linecard-disjoint: 40 default
• paths in RIB (ECMP or variance) are not considered as valid for backup

(config-router-af-topology)# fast-reroute per-prefix all|route-map <RMAP>

; use tie-breakers, off default ≡ several backups aka feasible successors
(config-router-af-topology)# fast-reroute load-sharing disable

(config-router-af-topology)# fast-reroute tie-break <RULE> <PRIORITY>

# show ip eigrp topology frr

Authentication

• key ID must match
• lower key ID is preferred
• authC change triggers neighbourship reset

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            0x0002             |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    AuthType   |   AuthLength  |   AuthData (variable length)  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

AuthType:

• 0x02: MD5
• 0x03: SHA

RIB scale

R1, R3 = numbered mode, R2 = named mode

1. 1.1.1.1/32 gets metric on R2, larger than 32bit ⇒ does not fit into RIB through RIB scale
2. R2 sends Query with correct metric components (not infinity!)
3. R3 updates its metric components from Query, responds with Reply
4. R2 has no route in RIB (FD = infinity), R3 installs new metric ⇒ blackhole
5. Further Updates from R2 do not remove 1.1.1.1/32

; 128 default, named mode only, 64bit → 32bit (size of RIB metric)
(config-router)# metric rib-scale <N>

Redistribute

Redistribute OSPF → EIGRP + no ip next-hop-self ⇒ next-hop in TLV = R3 (not valid for static)

; includes routes from RIB and connected routes of IGP-enabled interfaces
(config-router)# redistribute <IGP>

; metric is taken from egress interface (connected or leading to next-hop)
(config-router)# redistribute connected|static

; eBGP only by default
(config-router)# redistribute bgp

IPv6

; includes IGP-enabled prefixes as well
(config-router)# redistribute <IGP> include-connected

; 16 default
(config-router)# maximum-path <N>

; shutdown by default for numbered IPv6 EIGRP
(config-router)# no shutdown

Graceful restart

• router, that is going to restart, sends Hello with Kn = 255 and RS bit set
• neighbour purges stale entries after receiving EOT bit
• if there is no GR, neighbourship would flap → causes Query

(config-router)# nsf

; 240s default, NSF-aware, time to store routes from neighbour, who started graceful restart
(config-router)# timers graceful-restart purge-time <sec>

MPLS

• MP-BGP carries EIGRP information of a prefix in extended communities
  • communities
    • 0x8800: flags, tag
    • 0x8801: ASN, delay
    • 0x8802: reliability, hop count, BW
    • 0x8803: reserved, load, MTU
    • 0x8804: remote ASN, remote RID
    • 0x8805: remote protocol, remote metric
    • 0x8806: originating RID
  • internal prefix is completely restored from extended communities if ASNs match (otherwise – regular redistribute ≡ external prefix)
  • default-metric is still required
• protection against loops and count-to-infinity
  1. pre-bestpath cost community
  2. Site of Origin (SoO)

Cost-community

• added by default on redistribute
• POI = 0 (pre-bestpath), default insertion – after IGP cost (RFC)
• community ID
  • 128: internal
  • 129: external
  • internal has more priority over external
• carried over iBGP and confederation eBGP
• if absent from other Update, value of 0x7fffffff is assumed
• by default, if cost-community wins, only metrics are compared (AD is not), best metric → RIB (EIGRP only)

; enables AD comparison between iBGP and EIGRP, does not add cost-community, VRF-only
(config-router-af)# no populate bgp-ext-comm

Site of Origin (SoO)

• BGP extended community
• place in network: VRF interface on PE, backdoor interface
• if prefix is received on interface with SoO configured:
  1. SoO configured = SoO on prefix → drop, because it is indicator of loop
  2. pass through otherwise
• SoO added to prefix:
  1. set by BGP only; set only once, not changed in transit
  2. preserved on import from BGP
  3. EIGRP Update is not appended with SoO on backdoor interfaces
• if SoO on prefix and interface match, EIGRP Update is still sent (supposed to be dropped on other side only – account for multiaccess backdoor)

(config-route-map)# set extcommunity soo <VALUE>

; VRF PE – set SoO, backdoor – filter EIGRP Update based on SoO
(config-if)# ip vrf sitemap <MAP>

AddPath

• announce several next-hops using extended attributes
• must be supported by both peers
• incompatible with variance
• split horizon and next-hop-self must be disabled
• named mode only
• no ECMP mode
  • by default first entry in topology table must be reachable via same interface
    • if true, next-hop is not set to own address
    • if prefix is announced to another tunnel and 1st entry has other interface than egress interface, next-hop is set to own address
  • no-ecmp-mode searches all entries in topology table
    • if there is an entry through egress interface – preserve next-hop
  • useful for dual-hub DMVPN deployment

R4 receives only one next-hop from R1.

If AddPath is enabled, R4 receives both next-hops: R2 and R3.

(config-router-af-interface)# no split-horizon
(config-router-af-interface)# no next-hop-self [no-ecmp-mode]

; 0 by default, number of extra paths
(config-router-af-interface)# add-path <N> 

Over-the-top (OTP)

• establish neighbourship with non-directly connected peers
• data plane – LISP (UDP 4343), DF bit
• Route Reflector:
  • establishes session with spokes
  • forwards Update between spoke without next-hop change: no split-horizon and no next-hop-self
• supports SGT
• named mode only
• metric for Update through LISP interface is modified on egress (usually on ingress)

; TTL = 100 by default, INTF must be enabled by network command
(config-router-af)# neighbor <IP> <INTF> remote [<MAX_HOPS>] lisp-encap

; RR config, INTF must be enabled by network command
(config-router-af)# remote-neighbors source <INTF> unicast-listen lisp-encap 

(config-router-af-topology)# cts propagate sgt

Conditional receive

• neighbour, that is lagging behind, may receive mcast Update(n+1) before receiving retransmitted unicast Update(n)
• TLVs
  1. Next Multicast Sequence
     • in Hello
     • sequence number of the next reliable mcast
     • neighbours switch to CR-mode
  2. Sequence
     • list of IPs that belong to lagging neighours
     • lagging neighbours do not switch to CR-mode
• CR flag: processed only by routers in CR-mode

ACL

• extended ACL for filtering match on: source IP, prefix
• extended ACL for redistribution on: prefix, mask

Maximum prefix

• limit the number of prefixes from neighbour
• if exceeded, tear down the adjacency, ignore temporarily and then retry
• if error persists, manual restart is required

; limit prefixes from mcast neighbour, THRESHOLD = 75% by default, generates warning
(config-router)# neighbor [<IP>] maximum-prefix <N> [<THRESHOLD>] [warning-only]

; disabled by default, with every error multiplies restart-time by 1.5 times
(config-router)# neighbor maximum-prefix <N> dampened

; 5 minutes by default, how long to ignore
(config-router)# neighbor maximum-prefix <N> restart <mins>

; 3 by default, how many times to try establish adjacency automatically
(config-router)# neighbor maximum-prefix <N> restart-count <M>

; 15 minutes by default, resets restart-count
(config-router)# neighbor maximum-prefix <N> reset-time <min>

(config-router-af-topology)# redistribute maximum-prefix <N> ...

; restore peering after restart-count is crossed
# clear ip route *
# clear ip eigrp neighbor
# clear eigrp address-family neighbor