In my previous post on diagram drawing I shared my idea on how to draw VLANs on Visio network diagrams. Here I want to go level up with network virtualization entities and show how I draw VRF instances.
A VRF consist of Layer-3 interface members. So to me it sounds logical to bind VRF symbols to Layer-3 interface symbols. This is how I do it:
Different VRF instances can be depicted with diferent colors to make them easily distinguishable on a drawing.
For many years I’ve been struggling to memorize OSPF LSA types. Finally, I have decided to create a lab that shows all those LSA types that are supported by Cisco in OSPFv2 (IPv4-OSPF).
Here is my lab topology:
According to the documentation LSA type 1 is sent by any router within the area and contains the information about its directly connected links.
To see it I start packet capture in R1 Fa0/0 interface and reset the OSPF process at R2 to provoke LSA flood. Theoretically I should see two Type 1 LSA coming from R2: one for link 10.0.2.0/30 and another one for 10.0.1.0/24.
Here is what actually appears:
Two LSAs. One with unicast destination and one destined to “ALL OSPF ROUTERS” multicast address. Both contain the same information:
The information on both links is passed inside one Type 1 LSA. Links are presented with their IDs. There is a proper alogithm to derive Link ID depending on link type, in case of Transit that appears in this LSA network it’s DR IP address. The reason why R2 sends two LSA probably has to do with Cisco implementation of OSPF and the fact that R2 has broadcast multicaccess segment connected to it’s Fa0/1 interface.
This is how Type 1 LSA has been sent:
Type 2 LSA is generated by DR elected for multiaccess segment to inform its neighbors about this segment existence. An example of such a segment is the interconnecion between R2 R3 and R4. From R2 we can see that R4 got elected as DR (it’s router ID is 172.16.2.1):
R2#sh ip ospf neighbor
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So putting capture on R2 fa0/0 and resetting its OSPF process we should get Type 2 LSA from R4 containing information on R2-R3-R4 segment. Here it is, packed together with some other LSAs:
Notice the subnet mask for the segment, DR ID (Advertising Router) and three attached router IDs.
So Type 2 LSA flow is the following:
LSA Type 2
This type of LSA then gets resent by all the routers within the area (in this example R2 will resend it to R1). Advertising router field within the LSA will retain its original value as R4 being the DR is the one responsible for the LSA.
Type 3 LSAs are sent by ABR. When a link-state change occurs within one of the areas connected to it, it sends this type of LSA to all the other areas thus notifying them about that change. For example, when R2 Fa0/0 link goes down we can expect R3 to notify R6 about this change with Type 3 LSA.
Setting capture for Fa0/0 on R6 and shutting down Fa0/0 on R2 we get the following:
Notice the Metric field value. Setting it to 16777215 (FFFFFF hexadecimal) is a way to mark link as unreachable and signal to other OSPF routers to withdraw its data from their databases.
R3 generates Type 3 LSA because it gets notified of the change by Type 1 LSA coming from R2. Here is the flow diagram:
Please note that the name “summary LSA” has nothing to do with route summarization feature. Nothing gets summarized here, at least by default.
Type 4 LSAs are also sent by ABR. By using them ABR notifies it’s connected areas about the presence of ASBR in any of these areas. In my topology R3(ABR) would notify R6 which is in Area 1 about the presence of R1(ASBR) in Area 0 using LSA of this type. Later on R6 will receive some external route information from R1 and the Type 5 LSA announcing this route will contain R1 Router ID, saying that this external network is behind R1. Data obtained by R6 from Type 4 LSA will tell it that R1 is behind R3.
What makes router an ASBR and thus provokes LSA Type 4 generation? It’s route redistribution from any other routing process or protocol into OSPF occurring at this router. In my topology R1 is an ASBR as it redistributes routes from RIP into OSPF.
So, again, R3, being an ABR, should notify R6 about the presence of R1 using Type 4 LSA. But how does R3 get to know that R1 is an ASBR and not just any common intra-area router? The answer is: R1 notifies everyone within Area 0 of itself being an ASBR by setting a special (E) flag in Type 1 LSAs it sends. Here it is:
Wireshark already interprets E flag set as “AS boundary router”.
So when R3 receives this LSA it sends Type 4 LSA to notify R6:
Advertising router field contains R3 Router-ID, Link State ID contains R1 (ASBR) Router ID.
Here is what the process looks like:
LSA Type 5 is used to advertise external routes in all the OSPF areas. External in this case means not calculated or generated by OSPF process, but redistributed from other routing protocols, redistributed static or connected routes. As an example route for 192.168.99.0/24 network should be advertised by R1 using this type of LSA.
Putting R7 Loopback0 interface into shutdown provokes LSA flooding out of R1 FastEthernet0/0 notifying it as unreachable. Here is the capture:
This LSA Type contains external routes information as well as Type 5 LSA. The difference is that Type 7 LSA is propagated across Not-so-Stubby area and Type 5 LSA is not. On ABR that connects NSSA to Backbone area Type 7 LSA gets converted into Type 5 LSA.
In my topology R5 should notify R4 about changes with interface Loopback0 (172.16.102.0/24 subnet) using this type of LSA.
Here is a Type 7 LSA sent by R5 on it’s Loopback0 shutdown:
and here is LSA 5 generated by R4 for Area0, containing information on the same link:
Previously to use hardware (PVDM-based) transcoding you needed to register DSPFarm on CUCM or CME. But what if you don’t use any of these call control platforms, just have a router working as CUBE and want to accept one call leg and set up another with a codec different from originating? Starting with CUBE 9.0 Cisco has introduced Local Transcoding Interface (LTI) feature that permits you to register transcoding DSPFarm profile on CUBE itself.
CUBE version is mapped to IOS version, some information on version correspondence can be found here. The exact CUBE version on your router can be verified with show cube status command.
The call flow I used to test the feature is the following:
Here is a configuration example:
voice-card 0dsp services dspfarmdspfarm profile 1 transcode universalcodec g729r8codec g729br8codec g711ulawcodec g711alawcodec g729ar8codec g729abr8maximum sessions 4associate application CUBE <--- this command makes the profile to register and interact with CUBEno shutdown <--- Don't forget this, the profile is shutdown by default |
First, checking that DSPFarm profile has registered successfully:
#show dspfarm profileDspfarm Profile ConfigurationProfile ID = 1, Service =Universal TRANSCODING, Resource ID = 1 Profile Description : Profile Service Mode : Non Secure Profile Admin State : UP Profile Operation State : ACTIVE Application : CUBE Status : ASSOCIATED Resource Provider : FLEX_DSPRM Status : UP Number of Resource Configured : 4 Number of Resources Out of Service : 0 Number of Resources Active : 0 Codec Configuration: num_of_codecs:6 Codec : g729r8, Maximum Packetization Period : 60 Codec : g729br8, Maximum Packetization Period : 60 Codec : g711ulaw, Maximum Packetization Period : 30 Codec : g711alaw, Maximum Packetization Period : 30 Codec : g729ar8, Maximum Packetization Period : 60 Codec : g729abr8, Maximum Packetization Period : 60 |
Then trying to establish the call.
After the remote party answered the call, we can see RTP streams for both call legs up:
#sh voip rtp connections VoIP RTP Port Usage Information:Max Ports Available: 8091, Ports Reserved: 101, Ports in Use: 2Port range not configured, Min: 16384, Max: 32767Ports Ports Ports Media-Address Range Available Reserved In-useDefault Address-Range 8091 101 2VoIP RTP active connections :No. CallId dstCallId LocalRTP RmtRTP LocalIP RemoteIP 1 510647 510648 17882 10012 X.X.X.6 X.X.X.1 2 510648 510647 17884 12818 Y.Y.Y.68 Y.Y.Y.147 Found 2 active RTP connections |
It doesn’t tell us though which codec both call legs are using. Show call active voice command does that:
#show call active voice brief
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Here are the active sessions on configured DSPFarm:
#show dspfarm allDspfarm Profile ConfigurationProfile ID = 1, Service =Universal TRANSCODING, Resource ID = 1 Profile Description : Profile Service Mode : Non Secure Profile Admin State : UP Profile Operation State : ACTIVE Application : CUBE Status : ASSOCIATED Resource Provider : FLEX_DSPRM Status : UP Number of Resource Configured : 4 Number of Resources Out of Service : 0 Number of Resources Active : 1 Codec Configuration: num_of_codecs:6 Codec : g729r8, Maximum Packetization Period : 60 Codec : g729br8, Maximum Packetization Period : 60 Codec : g711ulaw, Maximum Packetization Period : 30 Codec : g711alaw, Maximum Packetization Period : 30 Codec : g729ar8, Maximum Packetization Period : 60 Codec : g729abr8, Maximum Packetization Period : 60SLOT DSP VERSION STATUS CHNL USE TYPE RSC_ID BRIDGE_ID PKTS_TXED PKTS_RXED0 1 33.1.0 UP 1 USED xcode 1 510648 799 807 0 1 33.1.0 UP 1 USED xcode 1 510647 804 797 0 1 33.1.0 UP N/A FREE xcode 1 - - - 0 1 33.1.0 UP N/A FREE xcode 1 - - - 0 1 33.1.0 UP N/A FREE xcode 1 - - -Total number of DSPFARM DSP channel(s) 4 |
All the output below is taken using debug ccsip messages. Messages not related to codec negotiation are omitted.
First, CUBE receives SIP INVITE from Local IP PBX with SDP containing G.711 A-law and µ-law:
Received:v=0o=root 4037 4037 IN IP4 X.X.X.1s=sessionc=IN IP4 X.X.X.1t=0 0m=audio 10012 RTP/AVP 8 0 101a=rtpmap:8 PCMA/8000a=rtpmap:0 PCMU/8000a=rtpmap:101 telephone-event/8000a=fmtp:101 0-16a=ptime:20a=sendrecv |
Then it resends the INVITE to Remote IP PBX proposing the same codecs:
Sent: INVITE sip:3000@Y.Y.Y.147:5060 SIP/2.0Via: SIP/2.0/UDP Y.Y.Y.68:5060;branch=z9hG4bK24310A3Remote-Party-ID: "3309" <sip:3309@Y.Y.Y.68>;party=calling;screen=no;privacy=offFrom: "3309" <sip:3309@Y.Y.Y.68>;tag=12587968-2B6To: <sip:3000@Y.Y.Y.147>Date: Fri, 08 Jan 2016 15:14:29 GMTCall-ID: 58D34E27-B55111E5-9AFACBDC-E71387B6@Y.Y.Y.68Supported: 100rel,timer,resource-priority,replaces,sdp-anatMin-SE: 1800Cisco-Guid: 1490163159-3041989093-2599734236-3876816822User-Agent: Cisco-SIPGatewayAllow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTERCSeq: 101 INVITETimestamp: 1452266069Contact: <sip:3309@Y.Y.Y.68:5060>Call-Info: <sip:Y.Y.Y.68:5060>;method="NOTIFY;Event=telephone-event;Duration=2000"Expires: 180Allow-Events: telephone-eventMax-Forwards: 69Content-Type: application/sdpContent-Disposition: session;handling=requiredContent-Length: 289v=0o=CiscoSystemsSIP-GW-UserAgent 3992 8898 IN IP4 Y.Y.Y.68s=SIP Callc=IN IP4 Y.Y.Y.68t=0 0m=audio 17884 RTP/AVP 8 0 101 19c=IN IP4 Y.Y.Y.68a=rtpmap:8 PCMA/8000a=rtpmap:0 PCMU/8000a=rtpmap:101 telephone-event/8000a=fmtp:101 0-15a=rtpmap:19 CN/8000 |
The Remote PBX responds with an error message:
Received: |
The response means that some media capability (we know it’s a codec) is not acceptable at the remote end. RFC3261 says this type of message MAY include a description of media capabilities that weren’t accepted so this could have told us what exactly the remote end didn’t like, but unfortunately in this case it doesn’t.
Anyway, CUBE sends another INVITE message, proposing G.729 codec:
Sent: INVITE sip:3000@Y.Y.Y.147:5060 SIP/2.0Via: SIP/2.0/UDPY.Y.Y.68:5060;branch=z9hG4bK244210DRemote-Party-ID: "3309" <sip:3309@Y.Y.Y.68>;party=calling;screen=no;privacy=offFrom: "3309" <sip:%239193093803@Y.Y.Y.68>;tag=12587AFC-2DCTo: <sip:3000@Y.Y.Y.147>Date: Fri, 08 Jan 2016 15:14:29 GMTCall-ID: 58D34E27-B55111E5-9AFACBDC-E71387B6@Y.Y.Y.68Supported: 100rel,timer,resource-priority,replaces,sdp-anatMin-SE: 1800Cisco-Guid: 1490163159-3041989093-2599734236-3876816822User-Agent: Cisco-SIPGatewayAllow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTERCSeq: 102 INVITETimestamp: 1452266069Contact: <sip:3309@Y.Y.Y.68:5060>Call-Info: <sip:Y.Y.Y.68:5060>;method="NOTIFY;Event=telephone-event;Duration=2000"Expires: 180Allow-Events: telephone-eventMax-Forwards: 69Content-Type: application/sdpContent-Disposition: session;handling=requiredContent-Length: 337v=0o=CiscoSystemsSIP-GW-UserAgent 3992 8899 IN IP4 Y.Y.Y.68s=SIP Callc=IN IP4 Y.Y.Y.68t=0 0m=audio 17884 RTP/AVP 8 0 18 101 19c=IN IP4 Y.Y.Y.68a=rtpmap:8 PCMA/8000a=rtpmap:0 PCMU/8000a=rtpmap:18 G729/8000a=fmtp:18 annexb=yesa=rtpmap:101 telephone-event/8000a=fmtp:101 0-15a=rtpmap:19 CN/8000 |
which remote PBX accepts sending an OK response with acceptable media capabilities list including G.729. This actually happens when remote user picks up the phone. Here is the message:
Received: SIP/2.0 200 OKVia: SIP/2.0/UDP Y.Y.Y.68:5060;branch=z9hG4bK244210D;received=Y.Y.Y.68From: "3309" <sip:3309@Y.Y.Y.68>;tag=12587AFC-2DCTo: <sip:3000@Y.Y.Y.147>;tag=as25e69ab7Call-ID: 58D34E27-B55111E5-9AFACBDC-E71387B6@Y.Y.Y.68CSeq: 102 INVITEServer: Remote PBXAllow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH, MESSAGESupported: replaces, timerSession-Expires: 1800;refresher=uasContact: <sip:3000@Y.Y.Y.147:5060>Content-Type: application/sdpRequire: timerContent-Length: 263v=0o=root 1736022661 1736022661 IN IP4 Y.Y.Y.147s=Asterisk PBX 11.14.2c=IN IP4 Y.Y.Y.147t=0 0m=audio 12818 RTP/AVP 18 101a=rtpmap:18 G729/8000a=fmtp:18 annexb=noa=rtpmap:101 telephone-event/8000a=fmtp:101 0-16a=ptime:20a=sendrecv |
The call proceeds with two legs using different codecs as expected.
The whole flow looks the following way (Red bars mark messages listed above, the ones containing codecs information):
An error 488 Not acceptable here could be avoided by changing the outgoing dial-peer configuration. CUBE proposes G.711 codecs first because of the voice-class applied to its outgoing dial-peer. This voice-class lists the codecs with the following preference order:
voice class codec 3 codec preference 1 g711alaw codec preference 2 g711ulaw codec preference 3 g729r8 codec preference 4 g729br8 |
Changing the priority or leaving just G.729 will do the trick.
Continuing L2 across L3 topic started with post about L2TP.
Another easy-to-setup way to interconnect two Ethernet segments across Layer 3 network is EoMPLS, a particular case of AToM.
The diagram I used for my tests and the initial configuration are the same as in my previous post on L2TP.
| R2 | R3 |
interface FastEthernet0/0 description -= WAN =- ip address 115.0.0.2 255.255.255.252ip route 0.0.0.0 0.0.0.0 115.0.0.1 |
interface FastEthernet0/0 description -= WAN =- ip address 116.0.0.2 255.255.255.252ip route 0.0.0.0 0.0.0.0 116.0.0.1 |
To set up EoMPLS you need to have MPLS-enabled transport network in between the border routers. But if you don’t have this option, such as in case of interconnecting LAN segments across the internet you can just use GRE to make border routers look directly connected to each other across the tunnel. All the configurations are made for common Cisco IOS (not XE or XR).
GRE Tunnel uses outside physical interfaces IP addresses as source and destination:
| R2 | R3 |
interface Tunnel0 ip address 1.1.1.1 255.255.255.252 keepalive 1 3 tunnel source 115.0.0.2 tunnel destination 116.0.0.2 |
interface Tunnel0 ip address 1.1.1.2 255.255.255.252 keepalive 1 3 tunnel source 116.0.0.2 tunnel destination 115.0.0.2 |
Tunnel is up:
R3#sh ip int brief | inc Tunnel0Tunnel0 1.1.1.2 YES manual up up |
And we have R2 and R3 “directly connected”.
First, I have set up Loopback interfaces on both border routers:
R2
interface Loopback0 |
R3
interface Loopback0 |
To have connectivity between Loopback interfaces I have set up OSPF (one might use static routing as well):
R2
interface Tunnel0 ip ospf 100 area 0interface Loopback0 ip ospf 100 area 0 |
R3
interface Tunnel0 ip ospf 100 area 0interface Loopback0 ip ospf 100 area 0 |
So now both Loopback interfaces see each other:
R2#sh ip route ospf
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Enforce the LDP router-ID on both routers:
R2
mpls ldp router-id loop0 force |
R3
mpls ldp router-id loop0 force |
Enable label exchange over GRE Tunnel:
R2
int tunnel0mpls ip |
R3
int tunnel0mpls ip |
Now the LDP neighborship is established:
R2#sh mpls ldp neighbor Peer LDP Ident: 3.3.3.3:0; Local LDP Ident 2.2.2.2:0 TCP connection: 3.3.3.3.64467 - 2.2.2.2.646 State: Oper; Msgs sent/rcvd: 8/8; Downstream Up time: 00:00:12 LDP discovery sources: Tunnel0, Src IP addr: 1.1.1.2 Addresses bound to peer LDP Ident: 116.0.0.2 3.3.3.3 1.1.1.2R2#show mpls forwarding-tableLocal Outgoing Prefix Bytes Label Outgoing Next HopLabel Label or Tunnel Id Switched interface16 Pop Label 3.3.3.3/32 0 Tu0 point2point |
R3#sh mpls ldp nei Peer LDP Ident: 2.2.2.2:0; Local LDP Ident 3.3.3.3:0 TCP connection: 2.2.2.2.646 - 3.3.3.3.64467 State: Oper; Msgs sent/rcvd: 8/8; Downstream Up time: 00:00:32 LDP discovery sources: Tunnel0, Src IP addr: 1.1.1.1 Addresses bound to peer LDP Ident: 115.0.0.2 2.2.2.2 1.1.1.1R3#show mpls forwarding-tableLocal Outgoing Prefix Bytes Label Outgoing Next HopLabel Label or Tunnel Id Switched interface16 Pop Label 2.2.2.2/32 0 Tu0 point2point |
We see some label (16) in show mpls forwarding-table command output, but it’s not the the label that will be used for tunneling traffic. There will be a few words later in this post about MPLS labels use with EoMPLS.
Now we have the following:
Similarly to L2TPv3 we now configure the interconnection (Virtual Circuit) using xconnect.
R2
interface fastethernet2/0 |
R3
interface fastethernet2/0 |
Trying ping between hosts:
R4#ping 192.168.1.5
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And to the broadcast address:
R5#ping 255.255.255.255
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Checking that the Virtual Circuit is established:
R2#show mpls l2transport vc detailLocal interface: Fa2/0 up, line protocol up, Ethernet up |
R3#show mpls l2transport vc detail
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In both commands output above we see Virtual Circuit ID that we have configured (2222), it’s status (Up), and the tunnel label (17). This is an actual label used in traffic “encapsulation/decapsulation”. The encapsulation itself consists in appending the label to the packet sent across the tunnel.
Looking at the ping capture between R4 and R5 we can see how the packet is formed:
Both captures show ICMP packet inside the Ethernet frame. Above that comes the Label 17 which we saw in show mpls l2transport vc detail command output. This is so-called VC Label that actually identifies Layer 2 interconnection. Above that comes GRE header and then IPv4 header used to deliver packet from one border router to another. This configuration theoretically can be used to establish EoMPLS interconnection across any sort of Layer 3 WAN, i.e. to perform the same task as L2TPv3 usually does.
Here are the final configurations for both routers:
R2
mpls ldp router-id Loopback0 force!interface FastEthernet0/0 description -= WAN =- ip address 115.0.0.2 255.255.255.252!interface Loopback0 ip address 2.2.2.2 255.255.255.25!interface Tunnel0 ip address 1.1.1.1 255.255.255.252 keepalive 1 3 tunnel source 115.0.0.2 tunnel destination 116.0.0.2 ip ospf 100 area 0 mpls ip!interface Loopback0 ip ospf 100 area 0!interface fastethernet2/0 xconnect 3.3.3.3 2222 encapsulation mpls!ip route 0.0.0.0 0.0.0.0 115.0.0.1 |
R3
mpls ldp router-id Loopback0 force!interface FastEthernet0/0 description -= WAN =- ip address 116.0.0.2 255.255.255.252!interface Loopback0 ip address 3.3.3.3 255.255.255.255!interface Tunnel0 ip address 1.1.1.2 255.255.255.252 keepalive 1 3 tunnel source 116.0.0.2 tunnel destination 115.0.0.2!interface fastethernet2/0 xconnect 2.2.2.2 2222 encapsulation mpls ip ospf 100 area 0 mpls ip!interface Loopback0 ip ospf 100 area 0!ip route 0.0.0.0 0.0.0.0 116.0.0.1 |
The more general use case for EoMPLS is when a service provider uses it to give Layer 2 interconnectivity to its customer. The EoMPLS VC starts at one PE router, crosses the MPLS-enabled service provider network (a number of P routers) and gets terminated at another PE router. In this case instead of GRE the MPLS transport is used. The series of labels gets attached and popped from the packet above the VC label. The network diagram I used to emulate this looks the following:
This is how ICMP echo request from R5 to R6 (192.168.1.5 to 192.168.1.6) travels across the MPLS WAN:
R1 → R2
R2 → R3
R3 → R4
The packet carries two labels: the inner one identifies the VC as in previous case and the outer one is used to transport packet across the MPLS network. The outer label gets discarded on R3, because of penultimate-hop-popping so we don’t see it on R3 → R4 segment.
The outer label can easily change on the way, because it is local for each MPLS router interface. The captures above just show the case where both R1 and R2 got the same label (23) assigned for packets that are being forwarded towards 4.4.4.4/32 prefix. However it’s not always the case. Here is an example with echo reply packet going back from R6 to R5:
R4 → R3
R3 → R2
R2 → R1
Outer label gets switched from 18 to 16 and then discarded on R2. The inner label stays the same.
Here is a diagram showing the packet flow for echo-request and echo-reply:
I have been trying to elaborate a nice way to depict VLANs on network diagrams throughout all my career.
The last idea I came up with looks like this:
Each one of the shapes represents a VLAN. I use the colors together with numbers in order to make shapes easier to read as they appear on the different parts of my diagram.
Here are some VLAN interfaces configured on a Layer-3 switch:
And here is a dot1q trunk:
Guess what it means when 31 shape covers the line? Right! – A native VLAN. The three other VLANs whose shapes are above and below the line are tagged.
You may stockpile the VLAN shapes around the “trunk line” whichever way you want:
Here I colored some VLANs the same yellow color as they all correspond to wireless segment. Also VLANs 3510-3517 are grouped together because they are all used for the same SSID with VLAN Select.