Arista EOS/Networking Tips by Solomon Yang: October 2019

10/28/2019

EOS - Find the interfaces with the most flaps

bn302.12:40:24#show int phy | egrep '^Eth' | awk '{print $3, $1}' | sort -rn | head -10
479 Ethernet9/25/2
23 Ethernet9/11/1
5 Ethernet9/34/1
5 Ethernet3/34/1

BGP Oscillation (RFC 3345)

BGP Oscillation is common in the context of MED + RR, because,

BGP only advertise the best path and hide the full list.
Similar to RR, it is also with BGP confederation

RFC 3345 has a very good depiction of how it happens

And I converted it to a google slides for a better view

in RFC, there lists a couple of design options to avoid this kind of churn

In RFC 7964, advertises all available paths by using ADD-PATH
Always compare MED even from different AS;
Don't accept MED
Utilize other BGP attributes higher in the decision process. (a little risky, because if any prefix leaked w/o higher attribute and tied)
Assign a high IGP cost to inter-cluster-link

10/15/2019

AS_PATH and Community regexp tips

1. match certain # of as_path

ip as-path access-list SixAS permit ^._._._._._.$ any

2. community list for some specific ending number, like ending 123. Because there is a space at the end of comm list, so need an underscore _, like

ip community-list regexp Ending123 permit ^.*:.*123_$

10/08/2019

Router Server

References:

Router Server = Internet Exchange (IX) Route Server = eBGP RR

Used in internet exchange
eBGP RR, so no need a full mesh eBGP peering among all parties
Reduces configuration complexity and CPU/memory overhead on border routers

Requirements:

AS_PATH transparency:

RS doesn't append its own AS# in the AS_PATH
RS-client doesn't enforce first AS

Nexthop transparency:

doesn't change NRLI's NH

MED transparency:

doesn't change path MED

Path hiding:

Per RFC 4271, BGP only advertises the best path, and a later update will be considered as an implicit withdrawal of the existing path.
In RFC 7947, it does mention the "path hiding". So the RS only advertises the best path, which could slow down the convergence time

EOS configurations:

service routing protocols model multi-agent << must multi-agent

route-map rtmap-no-change-med permit 10

set metric +0 << keep metric unchanged

router bgp 10

router-id 10.255.255.251

neighbor RS-Client peer group

neighbor RS-Client next-hop-unchanged << NH unchanged

neighbor RS-Client as-path prepend-own disabled << no own as#

neighbor RS-Client route-map rtmap-not-change-med out << rtmap

neighbor RS-Client password 7 xLcnzAMGHkI=

neighbor RS-Client send-community

neighbor RS-Client maximum-routes 12000

neighbor 10.10.10.11 peer group RS-Client

neighbor 10.10.10.11 remote-as 11

How many prefixes received? Considering the following scenario:

3 peers advertising ONE prefix
2 route servers
And all 3 peers also have bilateral peering
Then should be 5

Router1.15:19:15#sh ip bgp 11.111.1.1

BGP routing table information for VRF default

Router identifier 180.255.255.1, local AS number 65100

BGP routing table entry for 11.111.1.1/32

Paths: 5 available

12 111

10.10.10.12 from 10.10.10.12 (10.255.255.12) << from R2

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP head, ECMP, best, ECMP contributor

Rx SAFI: Unicast

11 111

10.10.10.11 from 10.10.10.11 (10.255.255.11) << from R1

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP, ECMP contributor

Rx SAFI: Unicast

11 111

10.10.10.11 from 10.10.10.251 (10.255.255.251) << R1 vis RS1

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP, ECMP contributor

Rx SAFI: Unicast

11 111

10.10.10.11 from 10.10.10.252 (10.255.255.252) << R1 via RS2

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external, ECMP, ECMP contributor

Rx SAFI: Unicast

13 333 111

10.10.10.13 from 10.10.10.13 (10.255.255.13) << R3

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:19 ago, valid, external

Rx SAFI: Unicast

Let's shut down the private peering to R2. So you can see the RS1 and RS2 don't advertise R2's path.

Router.15:26:31(config-router-bgp)#sh ip bgp 11.111.1.1

BGP routing table information for VRF default

Router identifier 180.255.255.1, local AS number 65100

BGP routing table entry for 11.111.1.1/32

Paths: 4 available

11 111

10.10.10.11 from 10.10.10.252 (10.255.255.252) << RS2

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external, best

Rx SAFI: Unicast

11 111

10.10.10.11 from 10.10.10.251 (10.255.255.251) << RS1

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external

Rx SAFI: Unicast

11 111

10.10.10.11 from 10.10.10.11 (10.255.255.11) << R1

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external

Rx SAFI: Unicast

12 111

10.10.10.12 from 10.10.10.12 (10.255.255.12) << R2

Origin IGP, metric 100, localpref 100, weight 0, received 00:00:02 ago, valid, external

Rx SAFI: Unicast

10/03/2019

EOS: A quick alias to show the interfaces with most util%

bn302#bash Cli -p15 -c 'srnz' | awk '{print $5, $8, $1}' | sort -r | more
Mbps Kpps Port
1.6% 4.5% Et9/36/1
1.5% 4.3% Et3/36/1
0.7% 0.5% Et13/33/1
0.7% 0.4% Et12/36/2

or set it as an alias

srnzsort bash Cli -p15 -c 'srnz' | awk '{print $5, $8, $1}' | sort -r | head -n 6

Updated note: The above command works with interface names/description defined. If not, have to change awk '{print $5, $8, $1}' to awk '{print $4, $7, $1}'

hs486.11:32:15#srnz
Port Name Intvl In Mbps % In Kpps Out Mbps % Out Kpps
Et49/1 0:05 9870.4 100.0% 812 9860.3 99.9% 811

hs486.12:14:45#bash Cli -p15 -c 'srnz' | awk '{print $4, $7, $1}' | sort -r | more
In In Port
100.0% 99.9% Et50/1
100.0% 99.9% Et49/4

How about some interfaces with description, some don't? hm.... Let me think about it..... :-)