Network Troubleshooting
Cumulus Linux contains a number of command line and analytical tools to help you troubleshoot issues with your network.
Check Reachability Using ping
ping is used to check reachability of a host. ping also calculates
the time it takes for packets to travel the round trip. See man ping
for details.
To test the connection to an IPv4 host:
cumulus@switch:~$ ping 192.0.2.45
PING 192.0.2.45 (192.0.2.45) 56(84) bytes of data.
64 bytes from 192.0.2.45: icmp_req=1 ttl=53 time=40.4 ms
64 bytes from 192.0.2.45: icmp_req=2 ttl=53 time=39.6 ms
...
To test the connection to an IPv6 host:
cumulus@switch:~$ ping6 -I swp1 2001::db8:ff:fe00:2
PING 2001::db8:ff:fe00:2(2001::db8:ff:fe00:2) from 2001::db8:ff:fe00:1 swp1: 56 data bytes
64 bytes from 2001::db8:ff:fe00:2: icmp_seq=1 ttl=64 time=1.43 ms
64 bytes from 2001::db8:ff:fe00:2: icmp_seq=2 ttl=64 time=0.927 ms
When troubleshooting intermittent connectivity issues, it is helpful to send continuous pings to a host.
Print Route Trace Using traceroute
traceroute tracks the route that packets take from an IP network on
their way to a given host. See man traceroute for details.
To track the route to an IPv4 host:
cumulus@switch:~$ traceroute www.google.com
traceroute to www.google.com (74.125.239.49), 30 hops max, 60 byte packets
1 cumulusnetworks.com (192.168.1.1) 0.614 ms 0.863 ms 0.932 ms
...
5 core2-1-1-0.pao.net.google.com (198.32.176.31) 22.347 ms 22.584 ms 24.328 ms
6 216.239.49.250 (216.239.49.250) 24.371 ms 25.757 ms 25.987 ms
7 72.14.232.35 (72.14.232.35) 27.505 ms 22.925 ms 22.323 ms
8 nuq04s19-in-f17.1e100.net (74.125.239.49) 23.544 ms 21.851 ms 22.604 ms
Run Commands in a Non-default VRF
You can use ip vrf exec to run commands in a non-default VRF context.
This is particularly useful for network utilities like ping,
traceroute, and nslookup.
The full syntax is ip vrf exec <vrf-name> <command> <arguments>. For
example:
cumulus@switch:~$ sudo ip vrf exec Tenant1 nslookup google.com - 8.8.8.8
By default, ping/ping6 and traceroute/traceroute6 all use the
default VRF. This is done using a mechanism that checks the VRF context
of the current shell - which can be seen when you run ip vrf id - at
the time one of these commands is run. If the shell’s VRF context is
mgmt, then these commands are run in the default VRF context.
ping and traceroute have additional arguments that you can use to
specify an egress interface and/or a source address. In the default VRF,
the source interface flag (ping -I or traceroute -i) specifies the
egress interface for the ping/traceroute operation. However, you can
use the source interface flag instead to specify a non-default VRF to
use for the command. Doing so causes the routing lookup for the
destination address to occur in that VRF.
With ping -I, you can specify the source interface or the source IP
address, but you cannot use the flag more than once. Thus, you can
choose either an egress interface/VRF or a source IP address. For
traceroute, you can use traceroute -s to specify the source IP
address.
You gain some additional flexibility if you run ip vrf exec in
combination with ping/ping6 or traceroute/traceroute6, as the
VRF context is specified outside of the ping and traceroute
commands. This allows for the most granular control of ping and
traceroute, as you can specify both the VRF and the source interface
flag.
For ping, use the following syntax:
ip vrf exec <vrf-name> [ping|ping6] -I [<egress_interface> | <source_ip>] <destination_ip>
For example:
cumulus@switch:~$ sudo ip vrf exec Tenant1 ping -I swp1 8.8.8.8
cumulus@switch:~$ sudo ip vrf exec Tenant1 ping -I 192.0.1.1 8.8.8.8
cumulus@switch:~$ sudo ip vrf exec Tenant1 ping6 -I swp1 2001:4860:4860::8888
cumulus@switch:~$ sudo ip vrf exec Tenant1 ping6 -I 2001:db8::1 2001:4860:4860::8888
For traceroute, use the following syntax:
ip vrf exec <vrf-name> [traceroute|traceroute6] -i <egress_interface> -s <source_ip> <destination_ip>
For example:
cumulus@switch:~$ sudo ip vrf exec Tenant1 traceroute -i swp1 -s 192.0.1.1 8.8.8.8
cumulus@switch:~$ sudo ip vrf exec Tenant1 traceroute6 -i swp1 -s 2001:db8::1 2001:4860:4860::8888
Because the VRF context for ping and traceroute commands is
automatically shifted to the default VRF context, you must use the
source interface flag to specify the management VRF. Typically, this is
not an issue since there is only a single interface in the management
VRF - eth0 - and in most situations only a single IPv4 address or IPv6
global unicast address is assigned to it. But it is worth mentioning
since, as stated earlier, you cannot specify both a source interface and
a source IP address with ping -I.
Manipulate the System ARP Cache
arp manipulates or displays the kernel’s IPv4 network neighbor cache.
See man arp for details.
To display the ARP cache:
cumulus@switch:~$ arp -a
? (11.0.2.2) at 00:02:00:00:00:10 [ether] on swp3
? (11.0.3.2) at 00:02:00:00:00:01 [ether] on swp4
? (11.0.0.2) at 44:38:39:00:01:c1 [ether] on swp1
To delete an ARP cache entry:
cumulus@switch:~$ arp -d 11.0.2.2
cumulus@switch:~$ arp -a
? (11.0.2.2) at <incomplete> on swp3
? (11.0.3.2) at 00:02:00:00:00:01 [ether] on swp4
? (11.0.0.2) at 44:38:39:00:01:c1 [ether] on swp1
To add a static ARP cache entry:
cumulus@switch:~$ arp -s 11.0.2.2 00:02:00:00:00:10
cumulus@switch:~$ arp -a
? (11.0.2.2) at 00:02:00:00:00:10 [ether] PERM on swp3
? (11.0.3.2) at 00:02:00:00:00:01 [ether] on swp4
? (11.0.0.2) at 44:38:39:00:01:c1 [ether] on swp1
If you need to flush or remove and ARP entry for a specific interface, you can disable dynamic ARP learning:
cumulus@switch:~$ ip link set arp off dev INTERFACE
Generate Traffic Using mz
mz (or mausezahn) is a fast traffic generator. It can generate a large variety of packet types at high speed. See man mz for details.
For example, to send two sets of packets to TCP port 23 and 24, with source IP 11.0.0.1 and destination 11.0.0.2, do the following:
cumulus@switch:~$ sudo mz swp1 -A 11.0.0.1 -B 11.0.0.2 -c 2 -v -t tcp "dp=23-24"
Mausezahn 0.40 - (C) 2007-2010 by Herbert Haas - https://packages.debian.org/unstable/mz
Use at your own risk and responsibility!
-- Verbose mode --
This system supports a high resolution clock.
The clock resolution is 4000250 nanoseconds.
Mausezahn will send 4 frames...
IP: ver=4, len=40, tos=0, id=0, frag=0, ttl=255, proto=6, sum=0, SA=11.0.0.1, DA=11.0.0.2,
payload=[see next layer]
TCP: sp=0, dp=23, S=42, A=42, flags=0, win=10000, len=20, sum=0,
payload=
IP: ver=4, len=40, tos=0, id=0, frag=0, ttl=255, proto=6, sum=0, SA=11.0.0.1, DA=11.0.0.2,
payload=[see next layer]
TCP: sp=0, dp=24, S=42, A=42, flags=0, win=10000, len=20, sum=0,
payload=
IP: ver=4, len=40, tos=0, id=0, frag=0, ttl=255, proto=6, sum=0, SA=11.0.0.1, DA=11.0.0.2,
payload=[see next layer]
TCP: sp=0, dp=23, S=42, A=42, flags=0, win=10000, len=20, sum=0,
payload=
IP: ver=4, len=40, tos=0, id=0, frag=0, ttl=255, proto=6, sum=0, SA=11.0.0.1, DA=11.0.0.2,
payload=[see next layer]
TCP: sp=0, dp=24, S=42, A=42, flags=0, win=10000, len=20, sum=0,
payload=
Create Counter ACL Rules
In Linux, all ACL rules are always counted. To create an ACL rule for
counting purposes only, set the rule action to ACCEPT. See the
Netfilter
chapter for details on how to use cl-acltool to set up
iptables-/ip6tables-/ebtables-based ACLs.
Always place your rules files under /etc/cumulus/acl/policy.d/.
To count all packets going to a Web server:
cumulus@switch:~$ cat sample_count.rules
[iptables]
-A FORWARD -p tcp --dport 80 -j ACCEPT
cumulus@switch:~$ sudo cl-acltool -i -p sample_count.rules
Using user provided rule file sample_count.rules
Reading rule file sample_count.rules ...
Processing rules in file sample_count.rules ...
Installing acl policy... done.
cumulus@switch:~$ sudo iptables -L -v
Chain INPUT (policy ACCEPT 16 packets, 2224 bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
2 156 ACCEPT tcp -- any any anywhere anywhere tcp dpt:http
Chain OUTPUT (policy ACCEPT 44 packets, 8624 bytes)
pkts bytes target prot opt in out source destination
The -p option clears out all other rules, and the -i option is used
to reinstall all the rules.
Configure SPAN and ERSPAN
SPAN (Switched Port Analyzer) provides for the mirroring of all packets coming in from or going out of an interface (the SPAN source), and being copied and transmitted out of a local port (the SPAN destination) for monitoring. The SPAN destination port is also referred to as a mirror-to-port (MTP). The original packet is still switched, while a mirrored copy of the packet is sent out of the MTP.
ERSPAN (Encapsulated Remote SPAN) enables the mirrored packets to be sent to a monitoring node located anywhere across the routed network. The switch finds the outgoing port of the mirrored packets by doing a lookup of the destination IP address in its routing table. The original L2 packet is encapsulated with GRE for IP delivery. The encapsulated packets have the following format:
----------------------------------------------------------
| MAC_HEADER | IP_HEADER | GRE_HEADER | L2_Mirrored_Packet |
----------------------------------------------------------
- Mirrored traffic is not guaranteed. If the MTP is congested, mirrored packets might be discarded.
- A SPAN/ERSPAN destination interface that is oversubscribed might result in data plane buffer depletion and buffer drops. Exercise caution when enabling SPAN/ERSPAN when the aggregate speeds of all source ports exceeds the destination port. Selective SPAN is recommended when possible to limit traffic in this scenario.
SPAN and ERSPAN are configured via cl-acltool, the
same utility for security ACL configuration.
The match criteria for SPAN and ERSPAN is usually an interface; for more
granular match terms, use selective spanning. The
SPAN source interface can be a port, a subinterface or a bond interface.
Ingress traffic on interfaces can be matched, and on switches with Spectrum ASICs, egress traffic can be matched. See the
list of limitations below.
Cumulus Linux supports a maximum of 2 SPAN destinations. Multiple rules (SPAN sources) can point to the same SPAN destination, although a given SPAN source cannot specify 2 SPAN destinations. The SPAN destination (MTP) interface can be a physical port, a subinterface, or a bond interface. The SPAN/ERSPAN action is independent of security ACL actions. If packets match both a security ACL rule and a SPAN rule, both actions will be carried out.
Always place your rules files under /etc/cumulus/acl/policy.d/.
Limitations for SPAN/ERSPAN
- For Broadcom switches, Cumulus Linux supports a maximum of two SPAN destinations.
- Because SPAN and ERSPAN are done in hardware, eth0 is not supported as a destination.
- For Spectrum switches, Cumulus Linux supports only a single SPAN destination in atomic mode or three SPAN destinations in non-atomic mode.
- Multiple rules (SPAN sources) can point to the same SPAN destination, but a given SPAN source cannot specify two SPAN destinations.
- To configure SPAN or ERSPAN on a Tomahawk or Trident3 switch, you must enable non-atomic update mode.
- Spectrum switches reject SPAN ACL rules for an output interface that is a subinterface.
- Mirrored traffic is not guaranteed. If the MTP is congested, mirrored packets might be discarded.
- Cut-through mode is not supported for ERSPAN in Cumulus Linux on switches using Broadcom Tomahawk, Trident II+ and Trident II ASICs.
- On Broadcom switches, SPAN does not capture egress traffic.
- Cumulus Linux does not support IPv6 ERSPAN destinations.
- ERSPAN does not cause the kernel to send ARP requests to resolve the next hop for the ERSPAN destination. If an ARP entry for the destination/next hop does not already exist in the kernel, you need to manually resolve this before mirrored traffic is sent (using ping or arping).
Configure SPAN for Switch Ports
This section describes how to set up, install, verify and uninstall SPAN rules. In the examples that follow, you will span (mirror) switch port swp4 input traffic and swp4 output traffic to destination switch port swp19.
First, create a rules file in /etc/cumulus/acl/policy.d/:
cumulus@switch:~$ sudo bash -c 'cat <<EOF > /etc/cumulus/acl/policy.d/span.rules
[iptables]
-A FORWARD --in-interface swp4 -j SPAN --dport swp19
-A FORWARD --out-interface swp4 -j SPAN --dport swp19
EOF'
Using cl-acltool with the --out-interface rule applies to transit
traffic only; it does not apply to traffic sourced from the switch.
Next, verify all the rules that are currently installed:
cumulus@switch:~$ sudo iptables -L -v
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 DROP all -- swp+ any 240.0.0.0/5 anywhere
0 0 DROP all -- swp+ any loopback/8 anywhere
0 0 DROP all -- swp+ any base-address.mcast.net/8 anywhere
0 0 DROP all -- swp+ any 255.255.255.255 anywhere
0 0 SETCLASS ospf -- swp+ any anywhere anywhere SETCLASS class:7
0 0 POLICE ospf -- any any anywhere anywhere POLICE mode:pkt rate:2000 burst:2000
0 0 SETCLASS tcp -- swp+ any anywhere anywhere tcp dpt:bgp SETCLASS class:7
0 0 POLICE tcp -- any any anywhere anywhere tcp dpt:bgp POLICE mode:pkt rate:2000 burst:2000
0 0 SETCLASS tcp -- swp+ any anywhere anywhere tcp spt:bgp SETCLASS class:7
0 0 POLICE tcp -- any any anywhere anywhere tcp spt:bgp POLICE mode:pkt rate:2000 burst:2000
0 0 SETCLASS tcp -- swp+ any anywhere anywhere tcp dpt:5342 SETCLASS class:7
0 0 POLICE tcp -- any any anywhere anywhere tcp dpt:5342 POLICE mode:pkt rate:2000 burst:2000
0 0 SETCLASS tcp -- swp+ any anywhere anywhere tcp spt:5342 SETCLASS class:7
0 0 POLICE tcp -- any any anywhere anywhere tcp spt:5342 POLICE mode:pkt rate:2000 burst:2000
0 0 SETCLASS icmp -- swp+ any anywhere anywhere SETCLASS class:2
0 0 POLICE icmp -- any any anywhere anywhere POLICE mode:pkt rate:100 burst:40
15 5205 SETCLASS udp -- swp+ any anywhere anywhere udp dpts:bootps:bootpc SETCLASS class:2
11 3865 POLICE udp -- any any anywhere anywhere udp dpt:bootps POLICE mode:pkt rate:100 burst:100
0 0 POLICE udp -- any any anywhere anywhere udp dpt:bootpc POLICE mode:pkt rate:100 burst:100
0 0 SETCLASS tcp -- swp+ any anywhere anywhere tcp dpts:bootps:bootpc SETCLASS class:2
0 0 POLICE tcp -- any any anywhere anywhere tcp dpt:bootps POLICE mode:pkt rate:100 burst:100
0 0 POLICE tcp -- any any anywhere anywhere tcp dpt:bootpc POLICE mode:pkt rate:100 burst:100
17 1088 SETCLASS igmp -- swp+ any anywhere anywhere SETCLASS class:6
17 1156 POLICE igmp -- any any anywhere anywhere POLICE mode:pkt rate:300 burst:100
394 41060 POLICE all -- swp+ any anywhere anywhere ADDRTYPE match dst-type LOCAL POLICE mode:pkt rate:1000 burst:1000 class:0
0 0 POLICE all -- swp+ any anywhere anywhere ADDRTYPE match dst-type IPROUTER POLICE mode:pkt rate:400 burst:100 class:0
988 279K SETCLASS all -- swp+ any anywhere anywhere SETCLASS class:0
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 DROP all -- swp+ any 240.0.0.0/5 anywhere
0 0 DROP all -- swp+ any loopback/8 anywhere
0 0 DROP all -- swp+ any base-address.mcast.net/8 anywhere
0 0 DROP all -- swp+ any 255.255.255.255 anywhere
26864 4672K SPAN all -- swp4 any anywhere anywhere dport:swp19 <---- input packets on swp4
40722 47M SPAN all -- any swp4 anywhere anywhere dport:swp19 <---- output packets on swp4
Chain OUTPUT (policy ACCEPT 67398 packets, 5757K bytes)
pkts bytes target prot opt in out source destination
Install the rules:
cumulus@switch:~$ sudo cl-acltool -i
[sudo] password for cumulus:
Reading rule file /etc/cumulus/acl/policy.d/00control_plane.rules ...
Processing rules in file /etc/cumulus/acl/policy.d/00control_plane.rules ...
Reading rule file /etc/cumulus/acl/policy.d/99control_plane_catch_all.rules ...
Processing rules in file /etc/cumulus/acl/policy.d/99control_plane_catch_all.rules ...
Reading rule file /etc/cumulus/acl/policy.d/span.rules ...
Processing rules in file /etc/cumulus/acl/policy.d/span.rules ...
Installing acl policy
done.
Running the following command is incorrect and will remove all
existing control-plane rules or other installed rules and only install
the rules defined in span.rules:
cumulus@switch:~$ sudo cl-acltool -i -P /etc/cumulus/acl/policy.d/span.rules
Verify that the SPAN rules were installed:
cumulus@switch:~$ sudo cl-acltool -L all | grep SPAN
38025 7034K SPAN all -- swp4 any anywhere anywhere dport:swp19
50832 55M SPAN all -- any swp4 anywhere anywhere dport:swp19
SPAN Sessions that Reference an Outgoing Interface
SPAN sessions that reference an outgoing interface create the mirrored packets based on the ingress interface before the routing/switching decision. For example, the following rule captures traffic that is ultimately destined to leave swp2 but mirrors the packets when they arrive on swp3. The rule transmits packets that reference the original VLAN tag and source/destination MAC address at the time the packet is originally received on swp3.
-A FORWARD --out-interface swp2 -j SPAN --dport swp1
Configure SPAN for Bonds
This section describes how to configure SPAN for all packets going out
of bond0 locally to bond1.
First, create a rules file in /etc/cumulus/acl/policy.d/:
cumulus@switch:~$ sudo bash -c 'cat <<EOF > /etc/cumulus/acl/policy.d/span_bond.rules
[iptables]
-A FORWARD --out-interface bond0 -j SPAN --dport bond1
EOF'
Using cl-acltool with the --out-interface rule applies to transit
traffic only; it does not apply to traffic sourced from the switch.
Install the rules:
cumulus@switch:~$ sudo cl-acltool -i
[sudo] password for cumulus:
Reading rule file /etc/cumulus/acl/policy.d/00control_plane.rules ...
Processing rules in file /etc/cumulus/acl/policy.d/00control_plane.rules ...
Reading rule file /etc/cumulus/acl/policy.d/99control_plane_catch_all.rules ...
Processing rules in file /etc/cumulus/acl/policy.d/99control_plane_catch_all.rules ...
Reading rule file /etc/cumulus/acl/policy.d/span_bond.rules ...
Processing rules in file /etc/cumulus/acl/policy.d/span_bond.rules ...
Installing acl policy
done.
Verify that the SPAN rules were installed:
cumulus@switch:~$ sudo iptables -L -v | grep SPAN
19 1938 SPAN all -- any bond0 anywhere anywhere dport:bond1
Configure ERSPAN
This section describes how to configure ERSPAN for all packets coming in
from swp1 to 12.0.0.2.
Cut-through mode is not supported for ERSPAN in Cumulus Linux on switches using Broadcom Tomahawk, Trident II+ and Trident II ASICs.
Cut-through mode is supported for ERSPAN in Cumulus Linux on switches using Spectrum ASICs.
-
First, create a rules file in
/etc/cumulus/acl/policy.d/:cumulus@switch:~$ sudo bash -c 'cat <<EOF > /etc/cumulus/acl/policy.d/erspan.rules [iptables] -A FORWARD --in-interface swp1 -j ERSPAN --src-ip 12.0.0.1 --dst-ip 12.0.0.2 --ttl 64 EOF' -
Install the rules:
cumulus@switch:~$ sudo cl-acltool -i Reading rule file /etc/cumulus/acl/policy.d/00control_plane.rules ... Processing rules in file /etc/cumulus/acl/policy.d/00control_plane.rules ... Reading rule file /etc/cumulus/acl/policy.d/99control_plane_catch_all.rules ... Processing rules in file /etc/cumulus/acl/policy.d/99control_plane_catch_all.rules ... Reading rule file /etc/cumulus/acl/policy.d/erspan.rules ... Processing rules in file /etc/cumulus/acl/policy.d/erspan.rules ... Installing acl policy done. -
Verify that the ERSPAN rules were installed:
cumulus@switch:~$ sudo iptables -L -v | grep SPAN 69 6804 ERSPAN all -- swp1 any anywhere anywhere ERSPAN src-ip:12.0.0.1 dst-ip:12.0.0.2The
src-ipoption can be any IP address, whether it exists in the routing table or not. Thedst-ipoption must be an IP address reachable via the routing table. The destination IP address must be reachable from a front-panel port, and not the management port. Usepingorip route get <ip>to verify that the destination IP address is reachable. Setting the--ttloption is recommended.
If a SPAN destination IP address is not available, or if the interface type or types prevent using a laptop as a SPAN destination, read this knowledge base article for a workaround.
ERSPAN and Wireshark
- When using Wireshark to review the ERSPAN output, Wireshark may report the message “Unknown version, please report or test to use fake ERSPAN preference”, and the trace is unreadable. To resolve this, go into the General preferences for Wireshark, then go to Protocols > ERSPAN and check the Force to decode fake ERSPAN frame option.
- To set up a capture filter on the destination switch that filters for a specific IP protocol, use
ip.proto == 49to filter for GRE-encapsulated (IP protocol 49) traffic.
Selective Spanning
SPAN/ERSPAN traffic rules can be configured to limit the traffic that is spanned, to reduce the volume of copied data.
Cumulus Linux supports selective spanning for iptables only.
ip6tables and ebtables are not supported.
The following matching fields are supported:
- IPv4 SIP/DIP
- IP protocol
- L4 (TCP/UDP) src/dst port
- TCP flags
- An ingress port/wildcard (swp+) can be specified in addition
With ERSPAN, a maximum of two --src-ip --dst-ip pairs are supported.
Exceeding this limit produces an error when you install the rules with
cl-acltool.
SPAN Examples
-
To mirror forwarded packets from all ports matching SIP 20.0.1.0 and DIP 20.0.1.2 to port swp1s1:
-A FORWARD --in-interface swp+ -s 20.0.0.2 -d 20.0.1.2 -j SPAN --dport swp1s2 -
To mirror icmp packets from all ports to swp1s2:
-A FORWARD --in-interface swp+ -s 20.0.0.2 -p icmp -j SPAN --dport swp1s2 -
To mirror forwarded UDP packets received from port swp1s0, towards DIP 20.0.1.2 and destination port 53:
-A FORWARD --in-interface swp1s0 -d 20.0.1.2 -p udp --dport 53 -j SPAN --dport swp1s2 -
To mirror all forwarded TCP packets with only SYN set:
-A FORWARD --in-interface swp+ -p tcp --tcp-flags ALL SYN -j SPAN --dport swp1s2 -
To mirror all forwarded TCP packets with only FIN set:
-A FORWARD --in-interface swp+ -p tcp --tcp-flags ALL FIN -j SPAN --dport swp1s2
ERSPAN Examples
-
To mirror forwarded packets from all ports matching SIP 20.0.1.0 and DIP 20.0.1.2:
-A FORWARD --in-interface swp+ -s 20.0.0.2 -d 20.0.1.2 -j ERSPAN --src-ip 90.0.0.1 --dst-ip 20.0.2.2 -
To mirror ICMP packets from all ports:
-A FORWARD --in-interface swp+ -s 20.0.0.2 -p icmp -j ERSPAN --src-ip 90.0.0.1 --dst-ip 20.0.2.2 -
To mirror forwarded UDP packets received from port swp1s0, towards DIP 20.0.1.2 and destination port 53:
-A FORWARD --in-interface swp1s0 -d 20.0.1.2 -p udp --dport 53 -j ERSPAN --src-ip 90.0.0.1 --dst-ip 20.0.2.2 -
To mirror all forwarded TCP packets with only SYN set:
-A FORWARD --in-interface swp+ -p tcp --tcp-flags ALL SYN -j ERSPAN --src-ip 90.0.0.1 --dst-ip 20.0.2.2 -
To mirror all forwarded TCP packets with only FIN set:
-A FORWARD --in-interface swp+ -p tcp --tcp-flags ALL FIN -j ERSPAN --src-ip 90.0.0.1 --dst-ip 20.0.2.2
If you specify a VNI instead of a switch port while using selective ERSPAN, you
need to reverse the -s and -d parameters, as this traffic is being captured after
VXLAN decapsulation.
If the previous example was used with a VNI, you would specify the rule like this:
-A FORWARD --in-interface vni10 -s 20.0.1.2 -d 20.0.0.2 -j ERSPAN --src-ip 90.0.0.1 --dst-ip 20.0.2.2
Remove SPAN Rules
To remove your SPAN rules, run:
#Remove rules file:
cumulus@switch:~$ sudo rm /etc/cumulus/acl/policy.d/span.rules
#Reload the default rules
cumulus@switch:~$ sudo cl-acltool -i
cumulus@switch:~$
To verify that the SPAN rules were removed:
cumulus@switch:~$ sudo cl-acltool -L all | grep SPAN
cumulus@switch:~$
Monitor Control Plane Traffic with tcpdump
You can use tcpdump to monitor control plane traffic - traffic sent to
and coming from the switch CPUs. tcpdump does not monitor data
plane traffic; use cl-acltool instead (see above).
For more information on tcpdump, read the `tcpdump` documentation and the `tcpdump` man page.
The following example incorporates a few tcpdump options:
-
-i bond0, which captures packets from bond0 to the CPU and from the CPU to bond0 -
host 169.254.0.2, which filters for this IP address -
-c 10, which captures 10 packets then stopscumulus@switch:~$ sudo tcpdump -i bond0 host 169.254.0.2 -c 10 tcpdump: WARNING: bond0: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on bond0, link-type EN10MB (Ethernet), capture size 65535 bytes 16:24:42.532473 IP 169.254.0.2 > 169.254.0.1: ICMP echo request, id 27785, seq 6, length 64 16:24:42.532534 IP 169.254.0.1 > 169.254.0.2: ICMP echo reply, id 27785, seq 6, length 64 16:24:42.804155 IP 169.254.0.2.40210 > 169.254.0.1.5342: Flags [.], seq 266275591:266277039, ack 3813627681, win 58, options [nop,nop,TS val 590400681 ecr 530346691], length 1448 16:24:42.804228 IP 169.254.0.1.5342 > 169.254.0.2.40210: Flags [.], ack 1448, win 166, options [nop,nop,TS val 530348721 ecr 590400681], length 0 16:24:42.804267 IP 169.254.0.2.40210 > 169.254.0.1.5342: Flags [P.], seq 1448:1836, ack 1, win 58, options [nop,nop,TS val 590400681 ecr 530346691], length 388 16:24:42.804293 IP 169.254.0.1.5342 > 169.254.0.2.40210: Flags [.], ack 1836, win 165, options [nop,nop,TS val 530348721 ecr 590400681], length 0 16:24:43.532389 IP 169.254.0.2 > 169.254.0.1: ICMP echo request, id 27785, seq 7, length 64 16:24:43.532447 IP 169.254.0.1 > 169.254.0.2: ICMP echo reply, id 27785, seq 7, length 64 16:24:43.838652 IP 169.254.0.1.59951 > 169.254.0.2.5342: Flags [.], seq 2555144343:2555145791, ack 2067274882, win 58, options [nop,nop,TS val 530349755 ecr 590399688], length 1448 16:24:43.838692 IP 169.254.0.1.59951 > 169.254.0.2.5342: Flags [P.], seq 1448:1838, ack 1, win 58, options [nop,nop,TS val 530349755 ecr 590399688], length 390 10 packets captured 12 packets received by filter 0 packets dropped by kernel