doc: update pcap guide

Add note about PMD expects the network interfaces provided to be up,
documented behavior to set expectations right.

Also added minor fix.

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>

diff --git a/doc/guides/nics/pcap_ring.rst b/doc/guides/nics/pcap_ring.rst
index de47f68..7fd063c 100644 (file)
--- a/doc/guides/nics/pcap_ring.rst
+++ b/doc/guides/nics/pcap_ring.rst
@@ -5,7 +5,7 @@ Libpcap and Ring Based Poll Mode Drivers
 ========================================
 
 In addition to Poll Mode Drivers (PMDs) for physical and virtual hardware,
-the DPDK also includes two pure-software PMDs. These two drivers are:
+the DPDK also includes pure-software PMDs, two of these drivers are:
 
 *   A libpcap -based PMD (librte_pmd_pcap) that reads and writes packets using libpcap,
     - both from files on disk, as well as from physical NIC devices using standard Linux kernel drivers.
@@ -148,6 +148,12 @@ Otherwise, the first 512 packets from the input pcap file will be discarded by t
         --vdev 'net_pcap0,rx_pcap=file_rx.pcap,tx_pcap=file_tx.pcap' \
         -- --port-topology=chained --no-flush-rx
 
+.. note::
+
+   The network interface provided to the PMD should be up. The PMD will return
+   an error if interface is down, and the PMD itself won't change the status
+   of the external network interface.
+
 
 Rings-based PMD
 ~~~~~~~~~~~~~~~