Arista EOS/Networking Tips by Solomon Yang: November 2018

11/30/2018

Arista EOS, SSO support starts from 4.20.5F

On Sand platform, 7500R/E series. And 4.20.5F was released around Arp 2018. (bl)

We have 2 commands to check if system is sso-ready:

wait-for-warmup checks for any agent to be not ready
show redundancy stat is to ensure sso stage participating agents to be warm

And better to run these 2 commands on both sup:

bn302.10:49:50#wait-for-warmup

bn302.10:51:11#show redundancy states

my state = ACTIVE

peer state = STANDBY HOT

Unit = Primary

Unit ID = 1

Redundancy Protocol (Operational) = Stateful Switchover

Redundancy Protocol (Configured) = Stateful Switchover

Communications = Up

switchover completion timeout = 120.0 seconds (default)

Not ready for switchover (Agents not ready in standby supervisor)

Agents not ready =

Sand

Last switchover time = 10:00:13 ago

Last switchover reason = Supervisor has control of the active supervisor lock

bn302.10:51:16#sess peer-supervisor wait-for-warmup

bn302.10:51:29#sess peer-supervisor show redu stat

my state = STANDBY HOT

peer state = ACTIVE

Unit = Secondary

Unit ID = 2

Redundancy Protocol (Operational) = Stateful Switchover

Redundancy Protocol (Configured) = Stateful Switchover

Communications = Up

switchover completion timeout = 120.0 seconds (default)

Not ready for switchover (Agents not ready in standby supervisor)

Agents not ready =

Sand

11/29/2018

Arista Linux Essential (2)

Useful Utilities

Date/time

date +%Y%m%d-%H%M%S
Epoch - Linux born time

Sort

du -s /var/* | sort -n
-n: numeric order

Cut

cut -d: -f:1,6 /etc/password
-c: cut columns

Diff:

Cli -p15 -c "show run" | diff -y -w -B --suppress-common-lines - /mnt/flash/startup-config
-B --ingore-blank-lines
-y --side-by-side
-w --ignore-all-space

regexp:

greedy vs lazy, ? at the end of pattern

grep = global reg exp print

-i: ignore case
-v: inverse, not-matching
-A: print # lines AFTER matching
-B: print # lines BEFORE matching

sed = powerful stream editor

remove quotes: sed -e 's/"//g'
reverse ip address:

echo "10.20.30.40" | sed -e 's/$[0-9]+$\.$[0-9]+$\.$[0-9]+$\.$[0-9]+$/\4.\3.\2.\1/'
reverse A-record to fwd record

awk

awk -F: '{print $1, $6}
alias shmc show int | awk '/^[A-Z]/ { intf=$1 }

tar

tar czvf config.1.gz config.1

[admin@bn303 etc]$ Cli -p15 -c "show run" | diff -y -w -B --suppress-common-lines - /mnt/flash/startup-config

! Command: show running-config | ! Startup-config last modified at Wed Nov 28 17:01:44 2018 b

! device: bn303 (DCS-7512N, EOS-4.20.1F) | ! device: bn303 (DCS-7512N, EOS-4.20.10M)

Arista Linux Essentials (1)

From the course - "Arista Linux Essentials"

Linux Flavors

Linux Distribution = Distro

Generally includes:

Kernel
Package manager
GNU tools and libraries
Documentation
GUI

Debian

All Ubuntu are Debian distro

Gentoo

For power users
ChromeOS is based on Gentoo

Android:

Uses a Linux Kernel
NO GNU tools and libraries, like glibc

SUSE
Fedora:

Red Hat, CentOS
Oracle's Unix OS

Not Linux anymore because changing kernel

Arista EOS is Fedora Core

No change in kernel
ver 18 or 21 now

Bootup

Boot Loaders:

Same on all computers
Multi-stage

First: BIOS/POST

Stored in ROM or NVRAM
Initialize system hw

MBR (Master Boot Record, Boot Loader)

Not OS-specific
Examples: Coreboot, LILO, GRUB
@arista switch, Aboot = a mini linux
Point to VBR

VBR (Volume Boot Record) .... OS Boot .... Kernel
OS Boot

dmesg display kernel message buffer

Arista Boot:

Power On:

BIOS

Active partition

Aboot -> init
init -> boot-config
ctrl - C to stop Aboot calls kexec

EOS Kernel:

Aboot calls kexec

EOS Boot Stages

EOS Stage 1:

/mnt/flash/persist
boot hooks - patch, bug fix here
not change kernel, change boot

Hw Init:

FRU initialize
Cell type config - module/fixed, supervisor
hw device tree

EOS Stage 2:

Kernel modules
ProcMgr
SysDB
Launcher

Init/runLevel:

scripts in /etc/init.d
init <runlevel>

Package Management:

wget - a web client to download files

in aboot

curl - more protocol support, http/ftp/imap/scp/....

not in aboot

Package Managers:

different distros use different manager
Debian/Ubuntu

uses dpkg
format is .deb
advanced tool apt, manage dependencies
apt-get, manage installation

Fedors (EOS)

uses rpm
format is .rpm
yum manage dependencies
as Fedora 18, yum is replaced by dnf

sudo dnf install sysstat

Python Notes (3) - Beautiful Python Code by Raymond Hettinger

https://www.youtube.com/watch?v=OSGv2VnC0go

Faster and prettier code:

1. Looping backwards
for color in reversed(colors):
print color

2. Looping over collection and indices
for i, color in enumerate(colors):
print i, ":", color

3. Zip of 2 lists
for name, color in zip(names, colors):
print name, ":", color

! zip has higher memory req, prone to cache miss;
! in python 3.x, using izip instead of zip

4. Sorted list
for color in sorted(colors):
for color in sorted(colors, reverse=True):

def compare_length(c1, c2):
if len(c1) < len(c2): return -1
if len(c1) > len(c2): return 1
return 0

for color in sorted(colors, cmp=compare_length):
for color in sorted(colors, key=len):

Looping over a dict with keys and values:
for k,v in d.items(): # req. memory to store list
for k,v in d.iteritems(): # use iterator instead of mem

Counting with dict
d ={}
for color in colors:
d[color] = d.get(color, 0) + 1

d = defaultdict(int)
for color in colors:
d[color] += 1

Grouping with dictionaries:
# group the list by length
names = ['Raymond', 'Rachel', 'Matthew', 'Roger', 'Betty']

#old
d = {}
for name in names:
key = len(name)
if key not in d:
d[key] = []
d[key].append(name)

#1
d = {}
for name in names:
key = len(name)
d.setdefault(key, []).append(name)

#2
d = defaultdict(list)
for name in names:
key = len(name)
d[key].append(name)

Function calls with keyword arguments
twitter_search('@obama', False, 20, True)

twitter_search('@obama', retweets=False, numtweets=20,
popular=True)

Packing/Unpacking = simultaneous state updates

x, y, dx, dy = ( x + dx *t,

y + dy *t,

influence(m,x,y),

influence(m,x,y))

Concatenating strings

', '.join(names)

Updating sequences

names = ['Raymond', 'Rachel', 'Matthew', 'Roger', 'Betty']

del names[0]

names.pop(0)

names.insert(0, 'mark')

#==>

names = deque(['Raymond', 'Rachel', 'Matthew', 'Roger', 'Betty'])

del names[0]

names.popleft()

names.appendleft('mark')

Python Notes (2)

1. Sort:

sorted() vs list.sort()

Sorted() returns a new list vs list.sort() does in place.
list.sort() only for list. But sorted() for all iterables.

key function and (reverse=True)
Sorted by multiple elements, like by first item then 2nd.

>>> p = [[1,2,3],[3,2,1],[2,4,6],[1,2,5],[1,3,7],[3,1,0],[1,7,2]]
>>> p.sort(key=lambda x:(x[0], x[2]))
>>> p
[[1, 7, 2], [1, 2, 3], [1, 2, 5], [1, 3, 7], [2, 4, 6], [3, 1, 0], [3, 2, 1]]

Sorted by reversed plus asc

>>> p = [[1,2,3],[3,2,1],[2,4,6],[1,2,5],[1,3,7],[13,1,0],[-1,7,2]]
>>> p.sort(key=lambda x:(-x[0], x[2]))
>>> p
[[13, 1, 0], [3, 2, 1], [2, 4, 6], [1, 2, 3], [1, 2, 5], [1, 3, 7], [-1, 7, 2]]

2. SET:

1) No duplicate
2) No order
3) Sets contain only hashable items, for __contain__ method
4) Sets have operator like "-"

_set = set([1,2,3,3]) # (1,2,3)

s1 = set([1,2,3,4])

s2 = set([2,3,5])

l1 = [1,2,3,4]

l2 = [2,3,5]

s1 - s2

set([1, 4])

l1 - l2

Error

3. Variable length arguments in function call

positional argument with unknown number of arguments
def __func__(*args):
for count, item in enumerate(args):
print '{0}. {1}'.format(count, thing)

named arguments
def __func__(**kwargs):
for name, value in kwargs.items():
print '{0} = {1}' % (name, value)

TCL:
proc __proc__ {first args} {}

4. How to re-import python module in interactive mode
>>> from myrange import *
>>> for i in myrange(1,3,1):
... print i
...
1 <<<<< extra print out due to debug print
1
2

$ more myrange.py
class myrange:
def __init__(self, start, end, step):
self.start = start
self.end = end
self.step = step
print self.step <<<< need to remove this

Change the py file, and do 2 steps

>>> import myrange <<< need to import module for reload()

>>> reload(myrange)

>>> from myrange import *

>>> for i in myrange(1,3,1):

... print i

...

1 <<<< corrected

5. Python class class/instance/internal variables

啥叫class/instance/internal variables?
- classVar 是Object之间share，一个改，大家都改，也叫Static variable
- instanceVar，所以叫Self.instanceVar，就是object自己本地
- internal，就不说了

class Obj(object):
classVar = [10,20,30]
def __init__(self):
self.instanceVar = [1,2,3]
internalVar = [100,200,300]

o1 = Obj()
o2 = Obj()

o1.instanceVar.append(11)
o1.instanceVar.append(12)
o2.instanceVar.append(21)
o2.instanceVar.append(22)

print o1.instanceVar
print o2.instanceVar

o1.classVar.append(111)
o2.classVar.append(222)
print o1.classVar
print o2.classVar

Python Notes (1)

1. Python FAQ:
https://docs.python.org/2.7/faq/programming.html

2. Python module search path
https://docs.python.org/2.7/tutorial/modules.html#the-module-search-path

If you do an "import syslib", how does the python locate the library?

1. local directory <<<< surprised?!
2. PYTHONPATH

so if you have a locally mistaken syslib.py or syslib.pyc under the local directory, you gonna break this import. And if you see something wanky, print cmd.__file__ will be helpful (or cmd.__version__)

3. Python Set
https://docs.python.org/3/tutorial/datastructures.html#sets

{} and set() can be used to create set
But to create an empty one, must use set(), not {} which is to create a dictionary.
set_ = {0}

4. 3 Ways to delete an element in a list

1) most efficient - del List[idx]
2) less efficient if need to have the element - List.pop(idx)
3) lest effificient - slice, List[:i] + List[i+1:]

5. Python reduce, filter
>>> l = [1,2,3,4]
>>> reduce( (lambda x,y: x*10+y), l)
1234
>>> reduce( (lambda x,y: x*100+y), l)
1020304
>>> l = range(1, 100, 5)
>>> l
[1, 6, 11, 16, 21, 26, 31, 36, 41, 46, 51, 56, 61, 66, 71, 76, 81, 86, 91, 96]
>>> filter(lambda x:x%4, l)

[1, 6, 11, 21, 26, 31, 41, 46, 51, 61, 66, 71, 81, 86, 91]

6. Python Naming Convention

http://legacy.python.org/dev/peps/pep-0008/#code-lay-out

limit all lines to 79，docstring/comment to 72

class Rectangle(Blob):

    def __init__(self, width, height,
                 color='black', emphasis=None, highlight=0):
        if (width == 0 and height == 0 and
                color == 'red' and emphasis == 'strong' or
                highlight &gt; 100):
            raise ValueError("sorry, you lose")
        if width == 0 and height == 0 and (color == 'red' or
                                           emphasis is None):
            raise ValueError("I don't think so -- values are %s, %s" %
                             (width, height))
        Blob.__init__(self, width, height,
                      color, emphasis, highlight)

Module: short,

all-lower-case name, like pystock.py

Class: CapWords, like

StockHist, StockInfo, StockERHist

Function:

lower_case_with_underscore

Method and instance:

lower_case_with_underscore

Constants:

ALL_CAPITALS_WITH_UNDERSCORE

Internal attribute:

_single_leading_underscore
NOT imported.

empty sequence = FALSE, so

YES: if not seq:...
NO: if len(seq)

Attributes:

self.lower_case_with_underscore

11/16/2018

SR Policy Architecture

https://datatracker.ietf.org/doc/html/draft-filsfils-spring-segment-routing-policy-06.txt

SR Policy包括什么？

ID of SR Policy = <headend, color, endpoint>
1个Policy可以有多个Candidate Path，一个CP可以有多个SID-lists, 可以有weight for LB
Protocol origin of CP

10: PCEP;
20: BGP SR;
30: Local, CLI/Yang...

Originator of CP, 160b = 20B

= 4B AS# + 16B Addr (128b)
如果Addr是v4，就放在最后4B

Discriminator of CP, default 0, 这个是啥？一个就是seq#，作为tie-breaker
ID of CP = <protoOrig, originator, discrimator>
pref of CP = 100
Valid of CP, 就是SID是valid
Active CP

higher origin id
lower originator ip
higher discriminator

SR policy还可以有priority，就是有topology change, 先算那个

SR Policy 例子：

1个policy, <headend, color, endpoint>
2个CP，CP1 is active 因为preference 200
CP1有两个SID-List, 都installed in HW, 而且ECMP

验证 CP

An explicit CP with SID-list = 应该是指静态CP

为空
Weight = 0
1st SID不能resolve
non-1st SID of type 3~11 into MPLS Label or SRv6 SID? 什么意思
挺多的，还有最后一个不是prefix SID

Dynamic CP

Binding SID

非常关键的一个概念
= CP，SR的无缝衔接？
可以代表任何的interface, tunnel.

Steering:

这个是很关键的概念
Headend可以steer traffic，以下方式：

local BSID
Per-dest, 需要BGP
Per-flow?
PBR

如果SR Policy失效，就fall back to 普通的routing
SR Policy可以是Drop

BSID Steering

<B, L2, L3> 变成 <S1, S2, S3, L2, L3> 如果S1不是PHP

Per-Dest Steering:

这个一个是最常见的
BGP routes <prefix, N, ext-color-C, VPN-Label-V>
Valid SR Policy - <endPt = N, color = C> of SID-list <S1, S2, S3> and BSID B
如果都met，NH != N, 而是=SR policy P of BSID B.
收到prefix pkt, push <S1, S2, S3, V> label
一个BGP update里面可以有多个color, 如果有对应的policy with colors, 最终只有一个FIB，因为higher color prefered