11-05-2011 06:26 AM - edited 03-07-2019 03:14 AM
I recently came across this question:
Q) Sort the associated traffic types give below in the correct order, based on priority (highest to lowest priority COS value)
call signalling
voice
network management
video interactive
video streaming
ip routing
I tried searching the correct order, i am confused on what is the right order.
In the link http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSIntro.html
at section “Figure 1-5 Example Strategy for Expanding the Number of Classes of Service over Time ” it says the order as
voice
video interactive
video streaming
call signalling
ip routing
network management
Whereas in the same link on section “Table 1-1 Cisco QoS Baseline/Technical Marketing (Interim) Classification and Marking Recommendations” it says the order as
ip routing
voice
video interactive
video streaming
call signalling
network management
I’M Really confused on which is the appropriate answer w.r.t the question which is asking “based on priority(highest to lowest COS vlaue)”
Can someone help me to identify which one is right please……
Thank you.
Manjunath
11-05-2011 06:40 AM
Hi Manju,
The Figure 1-5 is basically a classification of Qos models in offereing. i.e how granular you would like you classes to be. you can have different class models. It depends on the requirements that your company might have.
For eg;: I can have just 3 classes
Realtime - Voice, Video,
Critical - Network, Routing protocols,call signalling etc
Best Effort - www, email, business data.
It doesnt mean that voice is more important than routing protocols but its just a classification. The table 1-1 seems correct to me. put it this way without ip routing and protocols etc how will you get end-end IP reachability? without this how will you send your voice or data across.
HTH
Kishore
11-05-2011 10:59 AM
Hi Kishore,
So do you means below sequence is valid and not the other one ??
ip routing
voice
video interactive
video streaming
call signalling
network management
Does the IOS recognize the routing protocols and mark them to priority of 6 automatically without any manual configuration from CLI ??
11-05-2011 06:49 PM
Hi Manju,
Both are talking about different aspects of Qos so both are correct in what they re saying.
Fig 1-5 is talking about how many classes you need etc
the table is talking about prioritizatiion
When you design qos, its recommended that your qos doesnt go above 75% of the total bandwith and leave the rest 25% for signaling traffic routing protocols etc. however, if you decide that you want to use 100% bandwidth for your data then you need to prioritise your network traffic too(routing protocols, signalling)etc
HTH
Regards,
Kishore
11-06-2011 04:26 AM
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Posting
In answer to:
Q) Sort the associated traffic types give below in the correct order, based on priority (highest to lowest priority COS value)
Normally the "correct" answer is:
However although the CoS values would normally be applied highest to lowest as I've listed above, it doesn't really matter as the CoS (or DSCP) are but tags for you to classify traffic into groups so that you can treat them differently.
In earlier QoS, there were relative priorities, i.e. CoS (or IP Prec) 7 is "better" than CoS (or IP Prec) 1, but newer QoS models often treat the traffic differently based on the marking with no assumed (for the most part) preference because of the marking itself. For example in current DSCP, scavenger traffic has a "better" marking than best effort but it normally receives less resources than best effort.
Ranking application traffic types, today, is done mainly to (hopefully) preserve the traffic treatment we desire if the traffic transits a device using the old IP Prec or CoS precedence QoS model.
Real world QoS doesn't work too well just based on relative priorities. For example, Voice (bearer) traffic has a higher marking than voice signally. In fact, the latter has a lower marking than most all other "special" traffic yet if voice signally doesn't get the network resources it needs usually the call will drop. Of course, the sound quality might be great right up to moment you get disconnected.
If the above we also see network management at the bottom, but if network management has insufficient resource, we might lose visibility into our network and then not know why network management stopped working and additionally not be able to tell why other applicaitions are no longer working too.
11-06-2011 05:08 AM
Hii Kishore and Joseph,
Thanks for explaning this
So its like we can play with cos vlaues however we want giving good treatment to traffic which are classified as low priority
But still i would like to get answer to this below question for better understanding...
The cos value/priority for ip routing is 6. So does the IOS recognize the routing protocols and mark them to cos value 6 automatically without any manual configuration from CLI ??
I think yes is the answer for my above question, but i am not confident.
11-06-2011 04:38 PM
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Posting
Don't recall IOS auto marking CoS but it does auto mark at least some routing protocols with IP Prec 6.
11-06-2011 05:12 PM
Hi Manju ,
By default the routing protocols are not Cos marked. You can check it by doing a wireshark capture and can check the DSCP settings.on the IP packet.
HTH
Kishore
11-06-2011 05:51 PM
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Posting
Kishore Chennupati wrote:
Hi Manju ,
By default the routing protocols are not Cos marked. You can check it by doing a wireshark capture and can check the DSCP settings.on the IP packet.
HTH
Kishore
Yes, try that for BGP and examine the ToS.
Router#sh ip bg neighbors
BGP neighbor is 192.168.2.1, remote AS 20, external link
BGP version 4, remote router ID 192.168.1.2
BGP state = Established, up for 00:01:31
Last read 00:01:31, last write 00:01:31, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
Message statistics:
InQ depth is 0
OutQ depth is 0
Sent Rcvd
Opens: 1 1
Notifications: 0 0
Updates: 0 0
Keepalives: 2 2
Route Refresh: 0 0
Total: 3 3
Default minimum time between advertisements runs is 30 seconds
For address family: IPv4 Unicast
BGP table version 1, neighbor version 6/0
Output queue size : 0
Index 1, Offset 0, Mask 0x2
1 update-group member
Sent Rcvd
Prefix activity: ---- ----
Prefixes Current: 0 0 (Consumes 0 bytes)
Prefixes total: 0 0
Implicit Withdraw: 0 0
Explicit Withdraw: 0 0
Used as bestpath: n/a 1
Used as multipath: n/a 0
Outbound Inbound
Local Policy Denied Prefixes: -------- -------
Total: 0 0
Number of NLRIs in the update sent: max 3, min 1
Address tracking is enabled, the RIB does have a route to 192.168.2.1
Connections established 1; dropped 0
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Connection is ECN Disabled, Minimum incoming TTL 0, Outgoing TTL 1
Local host: 192.168.2.2, Local port: 1025
Foreign host: 192.168.2.1, Foreign port: 179
Connection tableid (VRF): 0
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0xC69F4):
Timer Starts Wakeups Next
Retrans 0 0 0x0
TimeWait 0 0 0x0
AckHold 2 0 0x0
SendWnd 0 0 0x0
KeepAlive 2 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
Linger 0 0 0x0
ProcessQ 0 0 0x0
iss: 2057115318 snduna: 2057115748 sndnxt: 2057115748 sndwnd: 15955
irs: 3480424370 rcvnxt: 3480424751 rcvwnd: 16004 delrcvwnd: 380
SRTT: 259 ms, RTTO: 579 ms, RTV: 320 ms, KRTT: 0 ms
minRTT: 16 ms, maxRTT: 300 ms, ACK hold: 200 ms
Status Flags: passive open, gen tcbs
Option Flags: nagle, path mtu capable
IP Precedence value : 6
Datagrams (max data segment is 1460 bytes):
Rcvd: 3 (out of order: 0), with data: 0, total data bytes: 0
Sent: 3 (retransmit: 0, fastretransmit: 0, partialack: 0, Second Congestion: 0), with data: 0, total data bytes: 0
Packets received in fast path: 0, fast processed: 0, slow path: 0
fast lock acquisition failures: 0, slow path: 0
11-07-2011 02:24 AM
Hi JD,
Thanks for that. check this one out.
BGP local router ID : 192.168.240.48
Local AS number : 65011
Paths: 2 available, 1 best, 1 select
BGP routing table entry information of 10.36.33.0/24:
Network route.
From: 0.0.0.0 (0.0.0.0)
Route Duration: 00h00m45s
Direct Out-interface: Ethernet0/0/1
Original nexthop: 10.36.32.1
Qos information : 0x0
AS-path Nil, origin igp, MED 0, pref-val 0, valid, local, best, select, pre 60
Advertised to such 1 peers:
172.30.0.230
BGP routing table entry information of 10.36.33.0/24:
From: 172.30.0.230 (172.30.0.222)
Route Duration: 00h00m45s
Direct Out-interface: Ethernet0/0/1
Original nexthop: 172.30.0.230
Qos information : 0x0
AS-path 55410 55410 55410, origin igp, pref-val 0, valid, external, pre 255, not preferred for route type
Not advertised to any peer yet
11-07-2011 12:01 PM
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
I've setup a link between two test routers and enabled RIPv1, OSPF and BGP across it. Nothing else in config. Configs are:
interface FastEthernet0/0
ip address 192.168.1.1 255.255.255.0
duplex auto
speed auto
!
router ospf 10
log-adjacency-changes
network 192.168.1.0 0.0.0.255 area 0
!
router rip
network 192.168.1.0
!
router bgp 10
no synchronization
bgp log-neighbor-changes
neighbor 192.168.1.2 remote-as 20
no auto-summary
===============================
interface FastEthernet0/0
ip address 192.168.1.2 255.255.255.0
duplex auto
speed auto
!
router ospf 10
log-adjacency-changes
network 192.168.1.0 0.0.0.255 area 0
!
router rip
network 192.168.1.0
!
router bgp 20
no synchronization
bgp log-neighbor-changes
neighbor 192.168.1.1 remote-as 10
no auto-summary
Did a packet capture. Looks to me like IP Predence 6 (or DSCP CS6) set on all routing packets. Also did a ping across the link which shows ToS with BE. IOS version: Version 12.4(15)T14
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